Archive of Our Own

Chapter Text

The green soul glowed warm in its container, thrumming gently against Gaster’s fingertips. There was Save power here, and plenty of it. He stared into the green light for a few, longing moments before carrying it over to the machine. His hands trembled as he slotted the green soul into a compartment next to the others.

Four souls. At last.

“Let’s begin the test,” Gaster said, turning to Dr. Betas. “We will start at 2% power and slowly increase it from there. We must be careful not to overheat the machine.”

Dr. Betas fidgeted with his hands. He kept glancing nervously in the direction of the elevator.

“Sh-Shouldn’t we wait? Shouldn’t S-Sans be here for this?”

“Let him mope for awhile.” Gaster stepped over to a console near the machine. Tubes and wires snaked back and forth between the two. Gaster flicked a few switches and a few lights on the machine came on.

“I’m worried about him…it’s been over a day and h-he hasn’t even called.”

“He will be fine.”

Sans had vanished immediately after turning the human to the guards. He hadn’t contacted Gaster or anyone at the lab, and he hadn’t gone home. Papyrus had actually called earlier looking for him; Gaster had simply lied and told him that Sans was hung up at work. Sans needed some time, and Gaster could understand that. And if Sans was still gone after another day, Gaster could simply go collect him. He knew exactly where Sans was—holed up in a little corner of Waterfall. Gaster had been keeping an eye on him, in a sense, to make sure that Sans didn’t try anything else foolish. It was a simple enough thing these days to peer through time and space and locate the skeleton. Gaster’s left eye had been so helpful lately. There were even times that he could actually control it.

Gaster turned a dial on the console and the machine hummed to life. The souls began to glow brighter. Gaster smiled. This was the beginning.

“We will increase the power output by increments over the next six hours,” he said. “Another five hours and the machine should have absorbed enough of the souls’ energy. Then the testing will begin in earnest.”

Dr. Betas was already typing away on his computer, monitoring the machine’s progress.

“Everything looks good so far…”

“Of course. We have done everything right. Every eventuality has been accounted for.” Gaster folded his hands behind his back, watching the machine and its glowing souls. “We have come too far to fail now.”

***

Sans was back into work the following day. Gaster smiled to himself when he heard the elevator descending, then grinned openly when Sans walked out.

“There you are, Sans.” Gaster gestured expansively at the fully charged, fully operational time machine. “We were forced to begin without you. You are just in time for the first test. We shall certainly need your expertise.”

“Sans!” Dr. Betas rushed across the room and stopped just short of actually tackling the skeleton. “I was s-s-so worried! Dr. Gaster said you were o-okay, but… And Papyrus e-even called us, h-he had no idea where you w-were, he was worried and we h-had to tell him you were h-here…”

Dr. Betas wrapped Sans in a tight hug. Gaster watched them from the other end of the lab. This was a waste of time, but he could allow them their emotional little moment. They wouldn’t have many of those left, after all.

“Whoa, hey, Betas, it’s okay.” Sans patted Dr. Betas’s back gently. “I’m fine. Just needed to get away for a bit, that’s all. I went home last night, so don’t worry about Paps either. Sorry for not calling.”

“The human didn’t hurt y-you?”

“Nah.” Sans tugged himself out of the hug. “I’m fine. Not a scratch on me, see?”

Dr. Betas glanced back in Gaster’s direction, then whispered something else to Sans. Gaster narrowed his eyes, but it was too late. He had missed it, whatever it was. Sans responded with a small shake of his head.

“So.” Sans patted Dr. Betas on the shoulder and headed toward the machine, giving Gaster a wide berth. Now that he was closer, Gaster could see that the skeleton clearly hadn’t slept at all. He was more disheveled than usual.

“First test, yeah?” Sans stopped in front of the machine and put his hands on his hipbones. “Should be interesting. Charging it up wasn’t a problem?”

“None at all.”

“Some unusual hull vibrations b-but nothing really unexpected,” Dr. Betas said, coming to join Sans.

“Your designs to cause resonance between the souls and the machine’s systems proved most effective, Sans.”

Sans shrugged. “Just a matter of matching up sine waves. Not hard.”

Gaster came to stand behind them, giving them both space. It wasn’t like he had forgotten the last thing he had said to Sans before Sans had disappeared into Waterfall. In retrospect, perhaps he had overreacted. But it was either that, or allow Sans to let the human go. That simply was not an option.

Gaster wondered if Sans finally hated him. That might present a problem. The bigger problem, however, was whether or not Gaster could still trust Sans at all.

Sans looked past the machine. The four human souls were in their facets on the wall. Cyan, orange, blue and now green.

“Turned out to be green, huh?”

“Y-Yeah,” Dr. Betas said, rubbing the back of his neck. “The, uh, guys in m-magic tech were very excited. Green magic is the most powerful human soul-based magic they’ve s-seen.”

“Yeah…?”

“Its effects are twofold.” Gaster took a careful step closer to them. Sans finally turned and looked Gaster in the eye. Gaster paused.

Sans didn’t just look exhausted. He looked…

Resigned.

Sans stared up at Gaster. “…Go on. I’m listening.”

Gaster cleared his throat.

“It affects monster bullets as well as souls,” he said. “Green bullets take on a healing property. Incredible, really, that a human’s soul could contain healing magic.”

Sans gave a small, tired smile.

“Heh. Incredible.”

“When used on a soul, it pins the soul in place, similar to blue magic. The affected host then cannot move at all, and thus cannot attack, forcing the host to stand firm and defend. Also rather odd, for a human.”

Sans broke eye contact with Gaster, turning away to walk over to his desk. He practically collapsed into his chair. Sighing, he brought up the current data on the time machine and started looking it over.

“Kid did say he didn’t want to fight at all.”

Gaster didn’t believe that for a second.

“In any case, we have a test to run. Shall we begin?”

“By all means, Doc. Things look good over here.”

“A-Alright then.” Dr. Betas grinned as he walked over to the machine. He might be a nervous wreck lately, but even he was excited at the prospect of finally testing what he probably considered to be his life’s work. He spun the wheel on the machine’s hatch and pulled it open. There was a hiss as the hermetic seal was released. Dr. Betas looked up at the other two and held up a ballpoint pen.

“This is one of my good pens. S-So let’s hope this works, right?”

“It’s a giant step for pens everywhere,” Sans said, giving him a thumbs-up. “You think its pen-pals will be proud?”

Dr. Betas snorted and set the pen down on the floor inside the machine. He seemed to be savoring the moment. Gaster wished he would hurry up. His fingers were already hovering over his computer’s keyboard.

Dr. Betas shut the hatch and turned the wheel to seal it. He stepped back to his work station.

“Kinda wondering if we should have a blast shield,” Sans said. “Bit late for it but—”

“My magic will protect us. Don’t worry, Sans.” Gaster looked pointedly in Sans’s direction. “None of us will come to harm.”

Sans didn’t look at him. Gaster stifled a sigh and turned back to his computer.

“R-Ready.”

“Ready.”

“In three, two, one.”

Gaster typed in a command. The machine powered up with a high-pitched whine. The whine quickly became louder until it was a shriek that seemed to vibrate in Gaster’s mind. He winced and the images in his left eye shattered and multiplied until he was seeing thousands of time machines at once. He felt his eye come alight with magic. Pain seemed to echo through his eye and up the crack in his skull.

Gaster squeezed his left eye shut, trying to focus. Brilliant light flashed from inside the machine, accompanied by crashing sounds like muffled lightning. The machine shook. For several long, tense seconds, it seemed as if it was simply going to shake itself to pieces.

Then all at once it stopped. The light inside it vanished and the machine powered down. Gaster typed a few commands on his computer as the machine’s program began generating progress reports. The ache in his head slowly faded; Gaster opened his eye again.

“Well, dang. That was louder than I thought it would be.”

“That m-might have been too much power.”

“Only one way to find out. Open it up.”

Dr. Betas headed to the machine again, Gaster and Sans close behind. He gingerly laid a claw on the hatch wheel.

“It’s a little bit warm to the touch. I-I hope the heat shielding is holding up.”

“Open it.”

It had worked. Gaster was sure of it.

“M-Moment of truth!”

Dr. Betas turned the wheel and pulled open the hatch. Gaster’s smile vanished. There on the machine’s floor was a puddle of melted plastic, ink and metal. It was sparking with white monster magic.

“Oh dear…”

Sans stepped back, cursing under his breath.

Gaster felt his hands curl into fists of their own accord.

“W-Well, the first test was bound to be a failure, right?” Dr. Betas darted away to go find something to clean the mess. “W-We can adjust the power output and—”

“Are you quite certain this wasn’t a hardware failure?” Gaster said, tracking Dr. Betas’s movements.

“I-I mean it’s possible, but my designs—”

“This should have worked.”

He felt a tug at the sleeve of his lab coat and looked down to see Sans.

“Ease up, Doc. This was just the first test. Like he said, it was bound to…Doc, your eye.”

Gaster blinked and reached up to cover his left eye. The glow hadn’t faded. Gaster gritted his teeth, trying to bring himself back under control.

Dr. Betas returned with a beaker and a bit of cardboard. The remains of the pen had cooled, giving the puddle a viscous quality. Dr. Betas managed to scrape the mess into the beaker, then sealed it.

“You gonna be alright, Doc?”

He could feel Sans watching him, waiting to see what he would do. Gaster wanted to snap at him. It seemed that Sans intended to keep on babysitting him, despite what Sans had tried to do. The hypocrite. But Gaster couldn’t yell at him. He needed Sans on his side.

“I am fine, Sans.”

He forced himself to calm down. Slowly the glow in his eye faded. He opened it again, taking a deep breath.

“I’ll run s-some tests on this,” Dr. Betas said, giving the beaker a small shake. “Maybe—”

“No. We will make some adjustments, lower the power output and try again,” Gaster said, going back to his desk. “Check the reports generated at your stations and make the proper fixes.”

“Doc, slow down. We—”

“We are running out of time.”

“Heh, isn’t that kind of the idea?”

“Really?” Gaster spun on him. “You are really making jokes right now?”

Sans stared at him for a moment, then sighed and gave a noncommittal shrug.

“It’s what I do.”

“Well I have no patience for it right now.”

“You have no patience for anything right now.”

“Do not test me, Sans.”

“No, right.” Sans chuckled a little. “We’re testing the machine, not you.”

Sans sat down at his desk and said nothing more. He went to work, clicking through some of the status reports on his computer. Gaster glared daggers at the back of Sans’s skull.

“Um, so…” Dr. Betas stood midway between the two of them, clutching the beaker and looking awkward. “Should I—?”

“Label the beaker and set it aside. We will analyze it later. Bring another pen.”

*** 

Gaster had stopped taking thorough notes on his work. He hadn’t written a full log in over a year. These days, his notes consisted of short, summarized entries in his notebook, and he often forgot to do even that. Everything he needed to know was already stored, in multiple forms, in his own mind. There seemed little point in writing anything down. Soon, this timeline would be gone. It wasn’t like he planned on bringing all of his notebooks back to the past with him. What would he possibly need them for?

Still, force of habit. He kept a short record of the tests on the time machine. Encoded in his own unique language, naturally.

Entry 2

           Machine cracked the lab floor halfway through test. Resulted in subject (ballpoint pen) melting into magic-infused ooze again.

           Failure again. We don’t have time for this. In a very literal sense, we do not have time.

           Lost temper. Broke chair with bullets.

           Chair? Wasn’t it a desk?

           No. Definitely chair. Perhaps in another timeline it was a desk (?)

           Sans was able to bring me down. Still quite angry with him for interference with regard to green soul. However, I am consistently forced to admit: he always knows what to say to pull me back.

           I will need him when I go through the dark.

Entry 4

           Took further precautions after last test’s short-circuit. Tests continue to leave subjects infused with magic. Odd. Subject (glass beaker) turned into sand. Progress??

           Feel calmer today.

           Asgore contacted me. First time talking in months. Was good to hear his voice.

Entry 5

           Why are the subjects infused with magic regardless of their original properties/the effects of Reset on them? This might present a problem when we move on to monster subjects. It doesn’t make sense. Possible side-effect of attempting to convert Reset into magic?

           Test subject (lead cube) melted.

           Checked Core again. A matter of days.

           Can feel my Save. Like an itch in the back of my mind. Almost wish I had never created it.

           Dr. Betas was acting suspicious today. They are always suspicious lately.

           What does he know? What are they hiding?

Entry 7

           It has been three days.

           Subject (iron ball bearing) melted. Infused with magic again.

           Can feel the Core. If it triggers before we are finished

           No time no time no

           Stay Determined.

Entry 9            

           Sans is the only one in this forsaken timeline who matters.

           And even then

           EVEN THEN.

           He still infuriates me.

           Subject (?????) melted, infused with magic.

           Lost temper. Broke something?

           Sans was there to keep me sane. Sane? Is that what this is?

           Dr. Betas had some kind of silly screaming fit. Would not stop YELLING. Left. Has not returned. Pathetic pathetic always knew he wasn’t worth my time.

           Sans is all I need.

Entry 10

           Breakthrough!

           Subject (notebook, college ruled) remained intact. Was still infused with magic. It seems that the subject becoming infused with magic is not preventable. Perhaps it will prove to be beneficial.

           Measurable tachyon particle activity within subject as well. Extremely promising.

           I am surprised that Dr. Betas was not present for this test. Nor did he join us later that night at Grillby’s. The machine would not have been possible if not for his skills as an engineer. Perhaps he is out sick?

           Or perhaps he is aware that soon he will no longer exist.

Entry ?

           Which timeline is this?

           Subject (mouse) did not survive the test.

           What a mess. Had Sans clean it up.

           HE SEEMS TROUBLED BY SOMETHING.

Entry 13

           Mistook the intern Alphys for Dr. Betas. Almost brought her down to the basement lab. Fortunately Sans corrected me. That would have been interesting to try and explain.

           Subject (mouse) did not survive. Less of a mess this time. Progress?

           The Core weighs heavily on my mind.

Entry 14

           Subject (mouse) survived the test but vanished soon after test’s completion. Disappeared into thin air. Presumably a result of tachyon particle overload. Subject has either traveled into another timeline or has been scattered among multiple timelines. No way of knowing.

           Everything seems to be going g o ing  GOING GOING GOING

           SHUT UP SANS.

           My notes seem to be a bit jumbled

           Or perhaps

Entry 16

           Subject (mouse) survived unharmed. Continued to show no ill effects after three

           No

           CAN’T TELL WHERE

           There was a small earthquake just now

           It is starting.

Entry 17

           DARK DARKER YET DARKER

           THE DARKNESS KEEPS GROWING

           THE SHADOWS CUTTING DEEPER

           PHOTON READINGS NEGATIVE

           THIS NEXT EXPERIMENT

           SEEMS

           VERY

           VERY

           INTERESTING

           …

           WHAT DO YOU TWO THINK?

***

Sans had not had a full night’s rest in two weeks now. Between the constant work with the time machine and his sheer inability to sleep, he had only managed to get a few hours at night and a nap here and there during the day. Over the last few days, Gaster had become completely intolerant of Sans’s naps, banging on his desk to wake him up whenever he drifted off.

The nights were always worse. At the end of the day he had to go home and face Papyrus, and every day Papyrus would ask how his day was, and every day Sans would lie. It was fine. Everything was fine. And yet Sans would lay in bed and stare at the ceiling and think about dead human children, or the violently shattered bodies of test mice, or of Gaster’s bullets throwing Dr. Betas against a wall, breaking his arm in three places.

The worst part wasn’t that Dr. Betas had had a nervous breakdown immediately thereafter and had quit the science division altogether. It wasn’t even Dr. Betas’s scream when it happened, or the sound of his bones breaking—the worst sound Sans had ever heard in his life. No, the worst part was that Gaster hadn’t even meant to do it.

The doctor had lost his temper, as he had done countless times over the past year. Sometimes he even summoned his bullets by accident, but even then, Gaster had always managed to keep a modicum of control. He had never fired his bullets at anyone—until now. And Dr. Betas had paid the price. He was lucky to be alive. He was lucky it hadn’t been a Gaster Blaster.

Sans had talked Gaster back down, like he always did, once he had been sure that Dr. Betas was physically stable. Gaster had seemed so confused afterwards. As if he hadn’t realized what he had done. Five days later he still didn’t seem to really understand. He kept addressing Dr. Betas as if he was still there.

Dr. Betas, at least, was doing much better. Sans had visited him at home. Sans hadn’t seen the poor guy that relaxed in years.

“At least one good thing c-came out of all this, right?” Dr. Betas had said. “Green magic makes it so much easier to use healing spells. M-My arm should be usable again in a few days.”

“Hey, I’m…sorry again. I couldn’t stop him in time.”

Dr. Betas shook his head, looking regretful.

“I’m just glad you stopped him before he could…keep g-going. And at least it wasn’t o-one of his Blasters, right?” Dr. Betas sighed heavily, sinking lower in his armchair. “It never should have g-gotten to this point, Sans.”

“Yeah…”

Dr. Betas looked at him with worried urgency. “You need to get out of there, Sans. While you s-still can.”

Sans folded his hands in his lap, lacing his fingerbones together.

“I can’t. He’s still my friend. I think I can still help him.”

“You’re trying so hard to save him, but w-who’s gonna save you?”

Sans had no answer for that.

“Just pr-promise me that you’ll be careful?”

“Heh. Always am. Anyway…we should probably stop talking about it. He might be watching me.”

The lack of sleep didn’t matter. The lies to his brother didn’t matter. Even the time machine didn’t matter. At this point, Sans no longer cared whether it worked or not. All that mattered was pulling Gaster back from the pit before him. Sans had to at least try.

The days since Dr. Betas quit had been rough. Gaster slipped away faster and easier. There were long stretches of hours during which he muttered to himself or communicated entirely in summoned bullets. Even when he talked normally his voice was becoming harder for Sans to understand. Sans had never had trouble with Gaster’s speech before now.

On the final day, the day of the eighteenth test, Sans arrived to work early. He didn’t know what had prompted him to do so. Afterward he would describe it as dumb luck.

Gaster was waiting for him in front of the elevator when the doors slid open on the basement level. The doctor smiled at Sans, his hands folded behind his back.

“Welcome, Sans. Are you ready?”

Sans smiled back despite his exhaustion. “For test eighteen? Lucky eighteen, right? You never actually explained what this test would entail. We moving onto monster subjects?”

Sans didn’t see anyone else in the lab, though, and it wasn’t like Gaster would be taking volunteers for a top secret, experimental project that could end with the monster melting or exploding. He looked past Gaster to where the time machine stood. It had been unhooked from the wall. He had a sinking feeling that Gaster was going to ask Sans to climb in there.

Or maybe he wouldn’t even ask.

“In a sense, but not quite. This next experiment will be…quite a lot more involved.” Gaster leaned down so he could put both hands on Sans’s shoulders. “Sans, I do not tell you this enough, but I have been eternally grateful for your help and loyalty. Your assistance has been indispensible these past few years.”

Sans blinked up at him. Whatever he had been expecting…this was not it.

“Oh.” He rubbed the back of his skull, heat climbing to his cheekbones. Gaster almost never sincerely complimented people. “I, uh. Thanks. I mean. It’s no problem. Er. I mean…”

Sans smiled a little, his first genuine smile in several days.

“It’s really been a pleasure working with you.”

“This experiment is going to change everything, Sans. It will be like nothing we have attempted thus far. We are going to Reset everything.”

“Already?”

“Yes. Everything is ready.”

The ground trembled. Sans started, looking around the lab. Fixtures shook on the walls and glass equipment rattled together. Another tremor? The Underground got earthquakes sometimes, but this was the second tremor in a week.

Gaster looked up as if he was seeing something else.

“It is time. I need to know that you are with me, Sans.”

“I…yeah. Till the end.”

“And beyond that, I hope!” Gaster chuckled a little, though Sans didn’t understand why. It wasn’t often that he missed a joke.

Gaster let go of Sans and stepped away, turning back toward the machine.

“Now. Let’s get the machine onto a maglev cart. We have a bit of a walk.”

“What? We’re taking it out of the lab?” Sans followed Gaster. “Is that safe? Where are we going?”

“To the Core.”

***

Sans pushed the machine while Gaster walked on ahead. He had been to the Core a thousand times before—you couldn’t get from Hotland to New Home without passing through the Core—but he had never been down this route before. There had been the usual amount of monster traffic on the road to the Core, and quite a few people had stopped to stare at them or ask them what was going on. They made quite a spectacle; the tall Royal Scientist walking ahead and not acknowledging anyone, and a short lab assistant pushing a ten-foot-tall machine floating a few inches off the ground on a maglev cart.

Sans waved off inquisitive Pyropes and Vulkins and Royal Guards by saying they were conducting a complex science experiment. Most people stopped listening when you mentioned science.

Once they got to the Core the traffic thinned out, which was strange. The Core was usually thick with monsters—if not travelers, then staff. But there seemed to be hardly any staff working today, which never happened. Sans had never seen the Core so empty and quiet. He couldn’t help but find it ominous.

“How deep are we going?” he finally asked when they had descended a third elevator.

“As deep as we can.” Gaster glanced back over his shoulder at Sans, smiling faintly. “Tiring out already, Sans?”

“You know me.” Sans mopped his forehead. “I’m always tired.”

“Do not worry. We are almost there.”

Sans looked around. This part of the Core was almost unrecognizable. The lighting was different from the main area, and there were none of the usual puzzles. The staff had completely vanished, leaving the Core seemingly devoid of life. Their footsteps echoed in the metal hallways.

“I didn’t even know this area existed,” Sans said, puffing a little as they stopped in front of yet another elevator. The maglev cart took away about 98% of the machine’s weight, but it was still heavy and difficult to navigate.

“There are many areas of the Core that no one still living knows about,” Gaster said, pressing the elevator call button. “I built many such places with my own two hands. So long ago, now. The purpose of the Core was always twofold. It provides power for the entire Underground, certainly. But the Core was meant to be so much more than that.”

Sans could hear the elevator clanking its way up from somewhere below. He leaned against the levitating machine and pulled out his phone to send a text to Dr. Betas. Dr. Betas wanted nothing more to do with Gaster or the experiments, but he had also wanted to be kept up to date. Just in case Gaster did something rash.

“So what’s the second thing, then?”

“Hm?”

“The second thing. You said the purpose of the Core was twofold.”

“Oh. Right.” The elevator pinged and the door creaked open. Gaster stepped aboard and Sans followed, pushing the time machine.

“The second purpose is what lies in the very bottom of—”

The floor began to shake, cutting Gaster off. Sans flailed and braced himself against the wall of the elevator. The elevator swayed to the side; Sans could hear it straining on its cables. The tremor continued for another few seconds before fading. The entire Core seemed to groan.

“Holy—two in one day?”

Gaster laughed and hit the only button in the elevator. The door slid closed.

“It’s getting feisty! Very soon, now.”

“Wait…are you saying that whatever’s down there is causing the earthquakes?” Sans stared at the floor, wishing he could see through to the bottom. The elevator began to descend.

“It is waking up. Sometimes I can almost believe that it is alive.”

Sans watched Gaster’s face. The doctor was smiling broadly. The elevator creaked as it descended. Sans looked at the floor again, starting to frown. There was a pressure growing behind his sternum, as if his nonexistent heart had started to pound.

“What’s really down there, Doc? What were you going to say before?”

“The Core is a power station, but it is also an engine. A magic engine, designed to concentrate ambient monster magic. Every time a monster has used their magic or summoned their bullets in the last thousand years, the energy left behind seeps into the air and ground. The Core is a geothermal power station. It does not just draw energy from heat and steam—it also siphons off that magic left behind and condenses it, gathering it in the room below.”

Gaster turned to Sans and grinned.

“I wish you could have been a part of this process, Sans, but I had to keep it a secret. You understand. But, oh, you would have found it all so very fascinating. Did you know that when condensed, monster magic changes color?”

Sans was growing nervous now. He could feel a cold sweat starting to prick along his bones.

“I…well, isn’t that how colored magic works?”

“Sort of. But when you concentrate magic past that point, it turns into something else. Not black, not really. It turns dark. A lack of not just color, but also light. I took some readings yesterday and found the photon levels to be completely nonexistent. Well—I needn’t say more. You will see.”

The elevator came to a stop and pinged. The door scraped open.

“That’s all pretty fascinating…” It was fascinating. Sans could write an entire thesis on these revelations. “I don’t get what this has to do with time travel and Reset, though…”

“Follow me.”

Gaster stepped out of the elevator. The room beyond him was virtually empty. There was nothing but a catwalk suspended above what Sans could only assume was the very bottom of the Core. It was warmer here than anywhere else; they had to be very close to the magma here. As Gaster stepped onto the catwalk, lights sprang on at strategic points along the railings. Overhead lights flickered to life as well. The ceiling was at least twenty feet above the catwalk.

Sans pushed the time machine out of the elevator. The catwalk was wide enough to allow the floating machine between the railings, still leaving a gap on either side. Once he was out, the elevator closed again and Sans was finally able to see the floor, several dozen feet below.

Only there was no floor.

There was nothing below the catwalk. No floor, no ground, no magma. The walls of the cavernous room descended into darkness. Everything beyond that point was pitch black, so dark it was like a hole in the world.

Sans froze. He had never been afraid of heights, but the darkness below him made him feel like he was standing above an impossible abyss. He let go of the machine and gripped a railing with both hands.

“What…Gaster, what…where are we…?”

Gaster laughed.

“Sans, you should see your face!”

Sans gripped the railings tighter, shaking a little. He couldn’t stop staring into it. The darkness below seemed to draw in light and devour it.

“Should I have warned you not to look down?” Gaster was still chuckling.“Don’t worry, Sans. You are not going to fall.”

“How is this possible?” Sans couldn’t bring himself to let go of the railing. He closed his eyes so he didn’t have to see it anymore. “That’s magic?”

“In a sense. Really, Sans, it’s not that bad. Let go. We need the machine to be positioned in the center.”

“I—sorry. Just. Give me a second.” Sans gritted his teeth. “It feels…wrong.”

He could feel it. The darkness was churning, even if it was impossible to see. It was like a heaviness on his mind.

“Nonsense. Come along. We don’t have time for this.”

Sans forced himself to open his eyesockets. He inhaled sharply when he saw the darkness again and tore his gaze away from it. This was wrong. Something about this was so wrong. What was this…thing doing here? What were they supposed to do with it?

Something gripped his hand. Sans flinched, startled, but it was only Gaster prying one of his hands away from the railing.

“I know it is unsettling,” Gaster said, voice stern. “But you said you would follow me. Until the end. Follow me now.”

Gaster gave him a tug. Sans took a breath and let go of the railing. Gaster kept hold of his hand and led him away down the catwalk. Sans hauled the time machine after him.

“You need to explain this to me, Doc,” Sans said, rather breathless. “I don’t understand. Why are we here? Why is that here? The Core has been…what, producing this thing the whole time?”

“Exactly correct. For over a thousand years now.”

Sans glanced downward again, then immediately looked away. He tried to focus on Gaster. His hand was solid in Sans’s own. Even so, it was difficult not to feel like he was falling. The closer they got to the center of the room, the more Sans could feel the hole below them. It felt so empty.

“But what for?”

“For this day. Here. Turn off the maglev and lower the machine onto the catwalk.”

At the center of the catwalk was a wider area with a control panel that presumably could retract the catwalk back toward the opposite walls.

Sans did as he was told, tugging his hand out of Gaster’s. The machine sank onto the metal grating of the catwalk. Sans shuddered as he felt the catwalk tremble.

“Don’t look so nervous, Sans! You look as nervous as Dr. Betas. Where is the old lizard, anyway?”

“He, uh. He quit, remember?”

“Ah. Right.”

“Doc.” Sans went back to holding onto the railing, just for security. “Tell me. What is all this? What are we doing?”

“The machine will produce Reset energy and will allow the occupants to travel back in time safely. That is what the tests up until now have all been for.”

“I get that, but—”

“The problem was always finding a pathway back to the beginning. Reset is not enough. It can only take one back so far. I told you I had the issue of the pathway covered, did I not?”

Sans remembered that conversation. He looked down. Gaster couldn’t possiblybe implying what he thought he was implying.

Gaster spread his hands over the darkness.

“This is our pathway.” He grinned. “Magic condensed to the point of darkness. Dense enough to punch a hole through spacetime, allowing someone to travel anywhere—or, excuse me, anywhen—that they wish. There is a similar concept in astrophysics, up on the Surface. When certain stars die, they collapse on themselves, leaving a gravity well from which nothing can escape. These ‘black holes’ are theorized to be tunnels to different points in spacetime. Ha! Of course, any attempt to enter a true black hole would result in the subject being reduced to as single stream of particles. The gravity is too strong—survival is impossible. This concentrated magic is much less deadly, though a lot less stable. Originally, my plan was simply to enter the darkness when it was large enough. But I soon discovered that doing so without proper shielding would result in almost certain death. A vessel would be required. A vessel in which the occupant could be safe from the tidal forces of magic and spacetime alike. Why do you think I was so pleased with your time machine designs? And why do you think I was so adamant about making sure it worked without damage to the occupant, inanimate or otherwise?”

Sans stared down into the dark, trying to process what Gaster was saying.

“You’re…” He closed his eyesockets and rubbed his forehead. “You’re saying that you’re going to…fly the machine into that.”

Gaster beamed at him. “Exactly! The dark magic provides the pathway. The machine takes care of the energy required, and of course, the destination. But not just me, Sans. We.”

Sans’s eyelights shrank to pinpricks.

“What?”

Gaster took hold of both of Sans’s hands.

“I want you to come with me, Sans.” Sans could feel him trembling with excitement. “Back to the beginning. To the war. You will be indispensible in the past, Sans. You have grown so strong.”

“I—I’m not that strong…” He wasn’t strong at all. Powerful, maybe, but not strong. “Gaster, this is…how do we even know this will work? All we’ve proven so far is that the machine works. And—it might not keep working. We haven’t even tested it with monster subjects yet. How do we know it will hold up under the stress of—whatever that is down there?”

“I have run numerous tests in secret, Sans. I have full confidence that this will work. It is a shame that we could not test the machine with monster subjects, but we have run out of time.”

“Yeah…y-you keep saying that.” Sans pulled his hands out of Gasters’. He took a step back, trying not to let his fear show on his face. “Why do you keep saying that? I always…thought it meant because eventually the Determination would get the better of you, but…it’s more than that, isn’t it?”

Gaster studied him with a mild expression. He was silent for a few long moments, staring through Sans. Another tremor rumbled through the Core, making the catwalk shiver. Sans held onto the railing for dear life. When the earthquake passed, Sans turned away and slipped his phone out of his pocket, carefully so as not to alert Gaster. Gaster was distracted enough that he didn’t notice Sans sending a text to Dr. Betas.

something is wrong. gather everyone you can. bottom of the core. might need to stop him.

“As perceptive as always, Sans,” Gaster said eventually. “The Determination was part of it. I can only assume that sometime soon I will lose control entirely. Though if I am quick, it might not even matter. It might even prove to be strategic, depending on what all this Determination will finally do to me.”

“Gaster, why are we out of time? Just tell me.”

“Ah…well, you may not like this part, Sans.” Gaster looked almost sheepish. Sans’s grip on the railing tightened until his knuckles hurt.

“Why are we out of time?”

“The darkness has reached maximum capacity,” Gaster said, turning away and staring down into the abyss. “The earthquakes will soon increase in number and intensity. When we activate the pathway and the machine begins to resonate with it, the Core will destabilize. The resulting explosion of magical and geothermal energy will destroy the Underground. I am no geologist, but I can only assume that most of the caves will collapse. Magma will flood the tunnels and rise.”

Gaster started laughing quietly.

“Ah, but the truly humorous thing—humans thought that trapping us under a mountain, with access to the heart of the planet, to the magma—we are only about a mile from the Earth’s mantle, did you know? Humans thought this was a good plan! And here we are, about to turn a mountain that should have remained a simple mountain for the remainder of its lifespan into a volcano! I wouldn’t be surprised if the mountain simply blew itself in half from all the pressure. Every human for miles will die.”

Gaster shrugged, still chuckling.

“Isn’t that hilarious, Sans? They trap us down here, and a few thousand years later, we send the literal underground right back up to meet them! Of course, every monster here will die as a result, but that seems a fair enough trade-off. Ah, I remember in the war, so many of them thought we were demons or some such nonsense. ‘Go back to hell!’ They screamed that as they slaughtered my family. ‘Go back to hell!’ And now here we are, bringing hell to them! Isn’t it funny, Sans? Why aren’t you laughing?”

Sans lurched backward, one hand clutching his chest, the other covering his mouth. He felt sick. He stared up at Gaster in horror.

Every monster. Every human for miles. Thousands upon thousands of people.

Gaster rolled his eyes.

“Don’t give me that look, Sans. Haven’t you figured it out by now? None of that is going to matter. You and I will be safely in the past. Once we Reset, this entire timeline, everything here, everything that has happened or is going to happen—it will all be destroyed. Erased. That is how this works. To create a new timeline, the old one must be deleted. Like moving a few files on your computer to the recycle bin.”

There was no earthquake, but Sans was shaking all the same. It felt as though the world was coming apart around him. His breaths came fast and shallow. Terror constricted around his bones.

“No…no, no, this…” Sans clutched the sides of his head. “This can’t be real. You can’t…you can’t be that fargone…”

Gaster frowned and took a step toward him. Sans scrambled backward and came up against the door of the machine.

“Listen to me, Sans. It is not like anyone will really die. You have no need to worry about that. When we Reset, it will simply be that none of this ever existed. No barrier, no Underground.”

“When…when the hell did you decide that this was an acceptable option?”

Gaster sighed in exasperation and folded his arms.

“I decided all of this a very long time ago. I have long since made my peace.”

“You’re talking about genocide!”

“Did you not hear me? I just said that no one will die. In fact, I assume that most of the monsters we know today will continue to exist in the new timeline’s future—just in vastly different ways. Don’t be melodramatic, Sans.”

“You have no way of knowing that! And we will be stuck in the past…in the middle of the war. Assuming the two of us could even do anything to stop the humans—”

Gaster grinned, and there was no mirth there. A simple baring of teeth, vicious.

“I believe that I will be able to handle them quite readily,” he said in a low, dangerous voice. “And you will be able to back me up. You have both types of blue magic. They won’t even know what has hit them.”

This couldn’t be real. This had to be some kind of nightmare.

“So…s-so you’re not just asking me to erase the timeline where everyone I have ever cared about lives…you’re not just asking me to help you destroy every living thing in range of the Core’s explosion…you’re also asking me to come back to the past, not…not for the pursuit of science, not to have an assistant, but because…because you want me to help you slaughter humans. Because I’ve gotten good at it. Am I…am I getting all that right?”

Gaster rubbed at his head as if Sans was giving him a headache. Vaguely, Sans hoped that he was. This was crazy. How could Gaster be serious about this? How could he have planned it all this way since the very beginning?

“That is hardly the reason, Sans.” Gaster stared at Sans, his expression somewhere between frustrated and…confused. Confused. He was confused about why Sans was reacting so strongly.

“Then what?”

“You are the only thing in this timeline worth sparing, Sans.”

Sans blinked at him for a moment in shock, then ground his teeth together and glared down into the abyss below.

“No,” he bit off. “No, you don’t get to say that to me. Everything you’ve done, everything you’ve asked of me…I can’t believe it. I can’t believe how stupid I’ve been. The only thing worth sparing? But this was your plan from the beginning. Since before you even met me.”

“No. That is not true. I did not understand the true nature of Reset until I made myself Determined. And when I created my Save, that was when I fully realized. The goal has always been to return to the past and stop all of this from ever happening. But it was not until recently I realized that it would result in this timeline’s destruction.”

Sans thrust a finger at him.

“Oh! Oh, but destroying the entire Underground by turning the mountain into afreaking volcano, that, that was always on the table!”

“I am growing tired of your melodrama, Sans. Yes, that was the very real eventuality when I first built this place. But again, it would not have mattered. My Resetting the timeline would have prevented that from ever happening. Have I not said this already? Do try to pay attention.”

Sans had never been so angry and so frightened in his entire life. He couldn’t even remember the last time he had even raised his voice.

“You keep saying it won’t matter! But what if all of this doesn’t work, Gaster? What if we do everything right and it just doesn’t work? Did you just trap us in a timeline in which the Underground is about to be destroyed?” Sans stopped short, narrowing his eyes. “No…you’re not that stupid. You’re not stupid at all. There…must still be a way to stop this. Am I wrong?”

Gaster didn’t answer, but the look on his face was that of a dangerous animal still deciding whether to bite.

“I knew it.” A relieved smile came to Sans’s face. “I knew it. There’s a way to stop this. We can shut all of this down.”

Gaster tilted his head.

“And why would I, exactly?”

“Because I’m asking you to.” Sans spread his hands. “I told you I would be there to pull you back, yeah? This is me pulling you back. I’m begging you, Gaster. We can’t do this. We can’t doom the entire Underground and any humans up there. We can’t just erase everything. You have to see how insane this is. Doc, please.”

Gaster didn’t answer, but Sans saw his eyes flick to the side. He was having doubts. He had to be.

Sans kept going.

“Please. Think about this. We either end up in the past, and everyone here dies, and we’re stuck with a war on our hands. I don’t…I don’t want to kill anyone else, Gaster. Human, monster. I’m sick of it. It’s either that or…or it doesn’t work, and we’re stuck here. We’re stuck here and everything we’ve worked toward doesn’t matter because everyone’s dead. Either way, everyone’s dead.” Sans covered his face with his hands. In his mind he could see it—miles and miles of gray dust and broken human bodies. The whole world destroyed. “Everything and everyone we love gone. Dr. Betas and Alphys, King Asgore, the whole science team. My brother…oh god, my brother…”

“Oh forget your idiot brother!”

Gaster stormed forward, crossing the distance between them in two strides. Sans tried to back away, forgetting he was against the machine. Gaster towered over him.

“It’s always your stupid brother,” Gaster snarled, his left eye coming alight with magic. “I am so utterly sick of hearing about Papyrus. I could never understand it. Is his stupidity meant to be charming? Is his complete lack of any useful, redeeming qualities meant to beendearing? How can you care about someone so completely pointless?”

“Sh—”

“I knew that skeleton would prove to be an obstacle. Pathetic.” Gaster pressed one hand to his head, fingers clawing against his scalp. He looked wild. “I should have had him killed.”

Something terrible and hollow opened inside Sans.

“Ga—”

“You would have been useless for awhile, but you would have gotten over it.” Gaster spread his arms wide, eye sparking. “All he has ever done is stifle you, Sans. All he has ever been is a burden.”

“Shut up. Shut up.” Sans tried to shove Gaster backward. Gaster didn’t even stumble. “You don’t know a goddamn thing.”

“It is the truth. You have simply never been willing to admit it.”

“You don’t get to talk about him like this! You don’t get to act like you somehow have my best interests at heart when you’re about to kill everyone!”

Sans tried to shove Gaster again. This time, Gaster caught Sans by his wrists and pushed him against the machine, pinning him in place. Sans let out a yelp of pain as the hatch wheel hit him in the spine.

“Pathetic,” Gaster said, voice soft. “Just like everyone else. Too attached to something so transient. From a certain point of view, I suppose you are right, Sans. Everyone is about to die. Papyrus included. When he’s gone, perhaps you will finally listen to me.”

“I’ll stop you.” He gasped as Gaster pushed him harder, making the wheel dig in between two of his vertebrae. Any harder and his back would break. “Ngh, please, Gaster, just stop this. You can stop this. W-We’ll think of something else, some other way t-to break the barrier…”

Gaster dug his thumbs in between the small bones in Sans’s wrists. Sans hissed in pain and struggled, squeezing his eyesockets shut.

“I can, but I won’t. I have come too far. Worked too hard. I cannot stop now.”

“Then I really will stop you. Th-That’s supposed to be my job, right? Hhhh, heh. Funny. Don’t remember that in the original job description.”

“How do you plan on stopping me, then? You are powerful, Sans, but not that powerful.”

“Dr. Betas is coming,” Sans growled, opening one eye. “Hopefully he’s not alone.”

“Is he, now?” Gaster dug his thumbs in deeper, until Sans cried out. “So in the end, you really did betray me.”

“I’m trying t-to save you, jackass. Think about this. Think about what you’redoing.”

“I have had a thousand years to think about it.”

“Hey, Doc.” Sans’s head lolled against his chest. He peered up at Gaster and grinned a little. “Did…d-did you hear the one about the doctor who fffff—who fell into a well?”

Gaster blinked at him.

“I beg your pardon?”

“Yeah. He should have focused on the sick and left the well alone.”

Ding.

Gaster’s soul turned blue and Sans shoved as hard as he could with his magic. Gaster didn’t even have time to react. He flew backward, tumbling head over heels, coming to a stop twenty feet down the catwalk.

Sans didn’t waste a second. He dropped to a crouch and whirled, switching the maglev cart back on. The time machine rose into the air. Sans darted around to the other side, grabbed hold of the edge of the cart and started pulling it back toward the elevator as fast as he could. If he could just get the time machine out of here, buy some time for Dr. Betas to arrive…

“SANS.”

“Oh god oh god oh god…”

Sans pulled faster, half-running, but the time machine was too heavy. The elevator was too far. He could hear Gaster’s footsteps rushing toward him. Gaster wouldn’t use his bullets, not so long as the time machine was between him and Sans.

Sans let out a shout of surprise as he saw a stream of hand-shaped bullets go shooting by past him. Apparently he had been wrong. The bullets crashed into the wall next to the elevator, leaving dents in the metal.

“GET BACK HERE, YOU CALCIFIED, PATHETIC EXCUSE FOR A MONSTER!”

Sans didn’t dare look back over his shoulder. The elevator was so close now.

Ding.

Sans stopped short, as if he had been frozen in place. He went rigid, completely unable to move. With an effort, he shifted his eyelights downward.

There was a green glow at his chest.

Gaster rounded the time machine and hit the button on the cart to drop the machine again. The cart was wrenched from Sans’s still outstretched hand. He tried to move—nothing happened.

Without even hesitating, Gaster grabbed Sans by the collar of his lab coat. He lifted Sans off the catwalk as if he weighed nothing, then tossed him away down the catwalk. Sans hit the metal hard. Sans tried to scramble to his feet, but halfway there Gaster simply took hold of his soul again. The feeling was a thousand times worse than blue magic. It was like his soul was in a vice grip, as if Gaster had physically wrapped his hand around Sans’s soul.

Sans looked up at Gaster. Gaster came to stand over him, one hand outstretched. His face was virtually unrecognizable.

“A fair enough attempt,” Gaster said, almost sounding impressed. “But at the end of the day, you are a failure.”

“G…Gaster…let me go.”

There was a sound. A sound that Sans knew too well.

A Gaster Blaster appeared. It opened its mouth and seemed to stare at Sans through glowing eyesockets, almost as though it was alive. Everything in Sans screamed at him to run, but he couldn’t move. He couldn’t move. He stared into the Gaster Blaster’s jaws, at the point of light already gathering in its throat.

“A failure, but still useful. A shame it had to come to this, but I need you, Sans.”

“No—please—”

“We are going to Reset now. You will come with me into the past. You will help me continue my work. You will do as I say, everything I ask of you, even if I have to permanently take control of your soul to do it.”

“Gaster, please.” Sans tried to move, but it was as if his bones had simply stopped working. He stared up at Gaster, meeting his eyes. “We’re friends. I’m your friend.”

“You’re my science project.”

Sans felt something break inside him. Not a bone. Something else.

“Yes. Nothing but a science project.”

“That’s…”

“A simple question I asked myself. Can I take this pathetic creature and make him useful?”

“Please…”

“What did you think I saw when I looked at you, Sans?”

“That’s not true.”

“I saw what everyone else sees. A small, lazy, useless excuse for a monster. Worthless. You were so happy when I gave you that power. So happy that you could finally be of use to someone. So happy that you could finally protect your equally worthless brother. What a sad little thing you must have been up until that day. The day I gave you power. The day I fixed you. And this is how you repay me.”

“Stop. This…this isn’t you. I know we—we’re—”

“There were so many experiments I wanted to try on you. I can’t for the life of me understand why I held back. Perhaps you can assist me with some of my theories after we have Reset, Sans. Once we have finished with the humans, I can turn my attentions to you fully. Will you still think of me as your friend when I have broken you apart and turned you into something truly wonderful? My little scientist turned science project. But don’t worry. I will keep you alive until…”

Gaster trailed off and frowned.

“What is that?”

He leaned closer.

“Are you crying, Sans?”

Sans tried to reach up to mop the tears away, but nothing happened. He never cried. Not in front of people. Not in front of anyone but Papyrus.

It really was pathetic. The world was coming to an end, everyone he had ever known was about to die, and yet this was the thing that broke him. He was Sans. He laughed things off, because the alternative was this. Crying solved nothing. It made everything hurt worse, and it showed the people around you just how weak you really were.

He could handle this from total strangers. He had handled it all his life. But hearing it from Gaster made all of this, everything that was happening, become all at once real. Everything was going to end. Gaster would pull Sans into the past and make Sans do exactly what he wanted. And Sans…was just Sans. A small, weak monster who couldn’t stop anyone. Not even his friend.

Maybe Gaster was right. Maybe they had never really been friends.

“Why would you…?” Gaster shook his head as if trying to clear the cobwebs from his mind. His lip curled. Another tremor rolled through the Core. “It doesn’t matter. We are out of time.”

Light continued to gather in the Gaster Blaster’s jaws.

“If you won’t come willingly, I will merely have to knock you out and force you. I suppose it will be easier for everyone if you are unconscious.”

“You’re going to kill me,” Sans said quietly, staring down the Blaster’s throat.

“Don’t be silly. I have more control than that.” Gaster smiled again, but there was a bit less vitriol in it this time. “It will certainly hurt like hell, though.”

Sans saw one last chance. One last glimmer of hope.

“If you shoot that thing at me, you’ll kill me.”

“Do you mean to tell me you won’t just dodge?” Gaster chuckled. “Oh, right! You can’t dodge if you can’t move. Seems your one skill is useless, Sans. Do be a good monster and hold still.”

The Gaster Blaster’s lower jaw split in half and it opened its mouth wide. The sound of gathering energy rose in pitch.

“No, you…you don’t understand.” Sans stared into the light. “I’ll die. E-Even if you hold back. I’ll be dust the—the second you fire. C-Can’t turn dust into a science project, can you?”

“Stop talking. Hold still.”

“Gaster, stop. Stop!”

“Just close your eyes. This is going to hurt.”

“Gaster!” Sans screamed his name. “I’ll die! I’ll die in one hit! I only have one HP!”

The sound of gathering magic plateaued. The Gaster Blaster stopped with its jaw unhinged, mouth full of light.

“Excuse me?”

“I-I only have one HP. P-Please. Please s-stop.”

Gaster frowned. The Gaster Blaster hovered at his side, ready to burst.

“Absurd,” Gaster said after a moment. “I made you strong.”

Sans made a snarling sound, furious, desperate, in pain.

“You made me powerful,” he spat. “You never made me strong. I’m as weak as I always was. You bastard. You never even noticed. You saw I could use magic and patted yourself on the back. Job done, right? You complete bastard. You s-stand there, ready to kill everyone, ready to erase the whole world. Ready to kill me.And you didn’t even know it. You say I’m the only thing worth sparing in this timeline, then you say I’m worthless, just a science project to you. You try to hurt me, and now you hesitate when I tell you I’ll actually die.”

Sans’s glare bore into Gaster’s eyes.

“You hypocrite! Make up your goddamn mind!”

Gaster pressed a hand to his head. “I…”

“Come on, Doc! What are you waiting for? Are you going to kill me or not? What am I gonna be to you, huh? Your friend? Your science project? Or a pile of dust?”

The Gaster Blaster vanished.

“No, no…this wasn’t supposed to…”

Gaster turned away, clutching his head and doubling over as if in pain. Sans looked down at his own chest. Still green.

“You were fine with destroying the whole world a second ago,” Sans’s said venomously. “What’s one more monster? Don’t kid yourself, Doc. You don’t really need me back there. All those human armies and wizards. You can take them all down yourself. Or you’ll find some other sadsack to torture and manipulate. Heck, if you wait long enough, you’ll even find another Sans. Then we can do this all over again. You gonna kill him too?”

“Shut up. Stop talking.”

Another tremor shook the room, making the catwalk sway.

“Come on, Doc. You’re out of time, remember? I’m not going with you. So you might as well just kill me.”

“I…I don’t…nnrrrgg…”

“You don’t what?” Sans let his voice soften. Almost. Almost there. “You don’t what, Gaster?”

Gaster gave a sad, strangled little noise.

All at once, the green glow at Sans’s chest vanished. He slumped back against the catwalk and curled into a shivering ball. The tears almost started again, just from sheer relief.

He peeked up at Gaster. The doctor was staring at his hands as if he had never seen them before.

“I…” He stopped. Looked around. He seemed to take in the machine, the catwalk, the darkness below. Finally his gaze settled on Sans.

“Sans…? What…what happened? I…” He clutched at his face. “What have I done? What did I say? God…oh my God. I could have…Sans, I almost killed you…”

“Yeah…” Sans rested his skull on the warm metal. “Got you to stop, though.”

Gaster took a step toward him. Sans scrambled backward and Gaster halted, watching Sans with a piteous look. He held up both hands, as if to show he meant no further harm.

“I am…so sorry, Sans.” Slowly, Gaster crouched down. Even slower, he offered Sans a hand. “I am so sorry.”

Sans looked between Gaster’s face and the offered hand. He started to reach forward, then hesitated, eyelights flicking to Gaster’s face again. Gaster made no further move toward him. His expression was pained. Heartbroken.

Sans reached out and took Gaster’s hand. Gaster pulled him onto his feet, then forward wrapping his arms around Sans. Sans tensed, certain it was another trick, but…

Gaster was hugging him. He was shaking.

“I am so sorry. For everything.”

“Hey…” Sans’s arms were too short to wrap around Gaster entirely, but he hugged back all the same. His fingers curled into Gaster’s lab coat.

“Hey, there he is.” Sans leaned his head on Gaster’s shoulder, face breaking into a sad smile. “Welcome back, Doc. It’s been awhile. I missed you.”

***

Gaster held onto Sans as if he was the last real thing in the world. Perhaps he was.

It had happened at last. Gaster had lost it. He had lost everything. He felt clear again for the first time in years. It wouldn’t last long. This was it.

The end.

The Core shook again, more violently this time. The catwalk groaned and swayed. Sans flinched in Gaster’s arms. Gaster held him tighter. There was a whirring sound as the elevator began to ascend. That would be Dr. Betas. He and whoever else had come to stop Gaster would be here in less than a minute.

“No…”

It was too late for them now. Too late to warn them.

“What have I done?”

“Hey.” Sans pulled back, just enough so that he could look Gaster in the eye. Gaster’s heart broke all over again upon seeing Sans’s face. The skeleton looked drained, exhausted, frightened. Broken. “There’s still time. We can stop it. Right? Just tell me what to do.”

“I think…that I am finished telling you what to do, Sans.”

“Doc—”

Gaster let go of him and stood. His left eye flickered nonstop, so he closed it. No distractions. He assessed. Analyzed. There were only a few seconds left to make a decision, and his options were sorely limited. The elevator had started to descend. No. No distractions. Dr. Betas and everyone aboard that elevator were already dead.

He looked at Sans. He looked at the time machine. He looked down into the dark.

“There is something I can do,” he said. “But—”

The world shook. The catwalk pitched upward, then down again as the wave cascaded through the Core. Gaster and Sans were thrown off their feet. There was a loud bang from the opposite end of the room as one of the struts connecting the catwalk to the wall came loose. The entire catwalk began to tilt.

“Whatever you’re going to do, do it fast!” Sans said, clinging to the railing as the catwalk leaned further and further to the left.

“I believe I can utilize my Save.”

“What, you’re…you’re gonna Reset back to your Save?”

“Not quite.”

Another earthquake. A second strut gave out with a scream of metal. The darkness swirled below them. Gaster wasn’t looking at it. He was staring at his hands. His fingers had begun to melt together. Determination had finally caught up with him.

“Time is up.”

Gaster extended a dripping hand toward the time machine, tipped over and wedged now between the railings. Hand-shaped bullets took hold of the hatch wheel and spun it, pulling the hatch open.

“What are you doing?” Sans cried, wrapping both arms around the railing as the catwalk began to sink and buckle. “You can’t—the timeline—!”

“I’m not.” Gaster could feel the rest of his body starting to melt. He could no longer feel his legs. “I can seal the darkness. Stop the destabilization. But you, Sans—you need to survive.”

“No, no, don’t you dare—don’t you—”

The catwalk groaned and buckled and Sans lost his grip. He fell down toward the darkness. Gaster let go of the railing and extended his hand. Sans’s soul turned blue and he stopped in midair, only a few feet above the dark.

“Gaster!”

“Remember your promise, Sans,” Gaster said, bracing whatever was left of his feet against the railing. “Now is the time for you to quit.”

“No, wait—”

Gaster yanked on Sans’s soul and tossed him upward into the time machine. He slammed the hatch closed behind him. Another burst of magic and the machine activated.

The elevator door opened. Dr. Betas and several others—scientists, guards—began to pour out.

 “Stay back!” Gaster cried, but it was too late. Two of them stumbled forward and fell, disappearing into the dark.

“Oh G-God!” Dr. Betas screamed, spreading his arms to keep anyone else from leaving the elevator. He looked up at Gaster. “Doctor, you need to stop this! Dr. Gaster!”

“I am,” Gaster said, gritting his teeth and tearing his eyes away. “I am so sorry, Dr. Betas. I will not be able to save you.”

Metal tore and began to shred. Gigantic cracks ran up the walls from the darkness below, splitting the elevator shaft to pieces. Sections of wall came loose and tumbled into the abyss. Lights exploded.

Another earthquake and the room collapsed. The catwalk finally gave way. Gaster heard Dr. Betas screaming.

In the final moment as everything fell, Gaster saw Sans’s face appear in the window of the time machine, saw his fists banging against the reinforced glass.

Gaster summoned a few of his bullets and spelled out two words.

He looked down at the darkness rushing up to meet him and smiled.

“Something needs to be done about that.”

The world went dark and Gaster felt himself shatter.

***

Spacetime tore like fabric. Gaster spread into every corner, slipping between the tears and seams. Determination kept Gaster alive and conscious. Just long enough.

With many hands, he took hold of each scattered piece of spacetime and pulled it back. He pulled the tears closed. Held the seams together.

Spacetime could heal, but not like this. The timeline would come apart again as soon as Gaster let go.

One last thing.

He reached for something bright. Took hold of it and cracked it open. It wouldn’t be enough to Save everything. No, not everything. But that was fine. The important parts would remain.

Slowly, spacetime began to knit back together. Slowly, the timeline began to reform.

It would hold.

They would be fine without him.

Gaster let go.

***

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