They didn't mention their conversation after that. Really, there just wasn't time. There was still a lot of work to do, and Sans needed to make as quick a recovery as possible to get back into it. The week following the experiment was the worst; he tried to work, but between the pain relievers and the lingering exhaustion, he couldn't force his brain to create equations, and the pages that soon littered the floor mostly comprised of incomprehensible scribbles and doodles.

True to his word as always, Papyrus was being an aggressively attentive nurse. The pain meds were given right when the next dose was due (and not any sooner!), mugs and bowls were whisked away as soon as they were emptied, encouraging notes were left on what Sans should do to maximize his recovery whenever Pap was out on patrols ("STEP ONE: TELL YOURSELF THAT YOU ARE GREAT (NOT AS GREAT AS ME, BUT THERE IS ALWAYS ROOM FOR IMPROVEMENT, BROTHER!!). STEP TWO: MAKE SURE YOU EAT A GOOD MEAL (THIS WILL BE BETTER WHEN UNDYNE TEACHES ME HOW TO COOK). STEP THREE: REPEAT STEP ONE, BUT THIS TIME DOING JUMPING JACKS.") , and, on the rare times where Sans wasn't asleep by the time night fell, Papyrus would break out "Peek-a-boo With Fluffy Bunny" and read to him. Sure, it was a little stifling, but Papyrus did make sure Sans was well-taken care of. Plus, the role-reversal was a bit of a reassurance—with Papyrus being Sans' caretaker instead of the other way round, Sans could believe that he was safe in the outside world.

As for Gaster, he dropped by a few times during the week, but wouldn't visit long. With Papyrus taking care of the medical stuff, Sans guessed he was putting his time into the amalgamates.

Regardless, he was going completely stir-crazy by the start of week two. It was time for an experiment. The past few days, he'd practiced teleporting pencils and mugs, half to see how he was faring and half for convenience. It didn't seem to affect him, so, hopefully, he could teleport downstairs. He wouldn't be able to do much—the few times he'd walked around the room left his bones aching—but it would at least be a change of scenery.

He focused hard on visualizing the sofa, thinking of exactly where to land—maybe it was overkill, but he'd rather not be found on the floor. He let out a breath, feeling the familiar surge of power—though a bit weaker than normal—and was dropped onto the couch a moment later. He grimaced at the initial impact, then relaxed with a contented sigh. Good to see that hypothesis worked; plus, teleporting seemed to take less energy than walking. Maybe he could teleport to the grey room? It wasn't as deep as the lower lab, but...

He sat up a bit as he heard voices in the kitchen.

"You almost have it. You simply need to flick your wrist a bit faster."

"Like this?"

"Yes! Yes, that is it exactly! Now try again."

It took a bit of effort and a bit of pain, but Sans was able to move his head enough to peek into the kitchen. His brow ridge rose as he saw Gaster and Papyrus; the latter was looking absolutely focused as his hands signed, with surprising clarity, "I AM DOING WELL TODAY!" (Somehow, even when using a silent method of communication, he managed to be loud.) Sans stretched his neck out a bit more, but his placement on the sofa wasn't as centered as he thought

The clatter of bones hitting the ground and a few choice words brought both of them rushing out as he pushed himself up and leaned back against the couch. Gaster opened his mouth, but Papyrus was quicker.

"Sans, what are you doing? You need to be in bed!"

Sans shrugged. "I, uh, decided to do an experiment." He nodded behind him. "You can see I didn't get sofa-r." With a grunt, he pulled himself up onto the couch. "See? I'm fine."

"You are NOT fine! We need to get you right back up--"

"How did you even get down here?" Gaster asked, lightly patting Papyrus' shoulder in apology as he cut him off.

Sans winked. "I took a shortcut."

Now it was Gaster's turn to worry. "You teleported? Sans, you are already in a fragile state and—"

Sans held up his hands. "I'm fine! Both of you, I'm fine. I'm still here, still solid, everything's good. I won't move anymore."

The other two skeletons both opened their mouths to protest, and Sans quickly changed the subject. "So, uh, looks like you're a natural with the language, Pap."

Papyrus's brow bone furrowed, and he shut his jaw as he thought over that. Suddenly his sockets widened. "Oh! The skeleton one!"

Gaster sent a somewhat annoyed look at Sans—he saw what he was doing—then let out a breath as he shook his head, trying to hide a small smile. "Well, part of that is because, unlike someone, he actually practices."

"Hey, I put a ton of work into the language." Sans winked. "A sk—" He was cut off as he was abruptly picked up and—as unceremoniously as possible while being careful—was slung on Papyrus' back.

"NO. TIME FOR BED."

"Papyrus, I just woke up." Sans turned to look back at Gaster, who was clearly trying not to laugh and showing no indication of helping him. "Seriously, the cops'll come soon if you don't put me back."

Papyrus stopped on the stairs, glancing back at Sans worriedly. "Really? Why?"

"Because I'm resisting a rest."

"SANS, I WILL DROP YOU."

"No, you won't."

"I WILL VERY SERIOUSLY CONSIDER IT!"

Sans laughed and gave up; at least he knew he could move around a bit, even if he had to wait for Papyrus to go out. He looked over his shoulder again. "See you later, Gaster!" He awkwardly turned and signed, "I be down here," before he winked.

Gaster smiled and gave a wave of acknowledgement. He watched the brothers argue for a moment longer, then let them be as he quietly slipped out of the house and to the grey room below.

~

It was quite a while before Gaster returned, but not without excitement. He burst into the house, waving notes in his mangled hands. "Sans, we must call Alphys, there is—!" The scientist frowned as he looked in the empty room. This is where he had said—Gaster checked his watch. Oh. It was later than he thought. He shook his head and made his way up the stairs, taking them two at a time. Regardless of the time, this was quite the development, and they needed to—

He opened the door, not bothering to knock, then stopped. Sans was in bed, fast asleep; he'd expected that. What he didn't expect was the quantum physics book in the snoozing skeleton's lap, or the pages and pages of equations and notes that were scattered all over the bed and the floor—he even still had a pen in his hand.

Despite the mountains of work around him, though, Sans looked quite peaceful. And so...small.

Gaster let out a breath, then looked down at his own notes. Well. It wasn't a life-threatening development. He supposed they could go over it in the morning. As quietly as he could, he walked over to take the pen from Sans' hand, setting it down with his notes for Sans to look over in the morning. He stopped for a moment, hand hovering over one particular paper. It wasn't equations, just a little drawing. Sans was prone to doodling when he thought, so it wasn't surprising.

All the same, Gaster took it.

He'd never had a family portrait before.

~

"I'm still really sorry I haven't visited!"

"Alph, you've been here for an hour. You can really stop apologizing. You didn't even need to apologize the first time."

"But still! I'm the worst friend!"

"No, you'd be the worst friend if you used my current condition to make me watch Mew Mew Kissy Cutie again." Sans used his pen to point at the television screen, where a cartoon about giant robots blowing stuff up was playing. "This is kinda cool."

Sans had found Gaster's notes when he'd woken up that morning—along with a smaller note assuring that they would discuss them after a DT meeting with Asgore. Not wanting to go through all this science alone, he had called Alphys over not much later; she wasted no time in coming, bringing along a bag full of videos and instant noodles as a "get well soon/sorry I'm part of the reason you're in a ton of pain right now" present. It would have been kind of fun—like a study party—except that the notes were all typed up in Gaster's strange language, making a quick skim impossible. Sans was able to translate them, yes, but it still took a lot of work. He slouched down in his seat with a huff.

"How does he even type this?" he grumbled. Alphys grimaced.

"Erm, my fault. I...well, see, he was getting really frustrated that he had to translate his notes before typing them up, so I, um, I made a program? With his alphabet?"

"Okay, that puts you in the running for 'worst friend'. You're making me do all this work." He scribbled down another line, then tapped his pen against his teeth. "All right, I've got the first page." He held up the paper. Around several scratched out misspellings, the following was written:

entry number seventeen

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?

The two of them looked over the page, silent for a couple minutes as they processed it. Sans finally shook his head.

"He's so dramatic."

Alphys snorted. "Sans! This is serious!"

Sans shrugged with a wink. "I'm making an educated observation." He looked at the paper again. "D'you know what he means by experiment?"

Alphys shrugged. "We haven't planned anything with the machine since you've been recovering."

Sans nodded, reading over the page again before he huffed. "He really didn't give us much to work with. Just...everything's dark."

Alphys pushed her glasses up a bit as she looked at the page. "Well, he's probably talking about the time gauge. You know, downstairs."

"Does that measure photons, though? It's, uh, that's light, right?" He grabbed the quantum physics book on the side-table, awkwardly flipping through it with one hand.

"Oh, god, right, you're still learning this stuff." Alphys puffed out her cheeks. "It's, um, well, it's...basically light and all other kinds of electromagnetic radiation? Because, um...god, I'm so bad at explaining this...well, okay, so it's hard to measure time, because it's, y'know, relative. Especially down here, since we kind of have to make up how long a day is. So the prototype, it, erm, it measures fluctuations of EM radiation...there's allowances for magic and stuff, but it should still stay pretty stable." She frowned, taking the paper from Sans to look at it again. "But if there was a reset—based on what you wrote—then there should have been a dip in the readings. It shouldn't have gone completely into the negatives. That'd be the absence of, well, anything."

Sans blinked. "So...did we just stop existing for a bit?" He tapped his pen to his jaw. "I would have felt a reset—after you've done one, you know what it feels like—but things have been steady."

Alphys shook her head, looking at the paper hard. "I don't know, I really don't. I think we're just gonna have to go through the rest of his notes."

Sans groaned, lightly hitting his head against the couch cushion, then let out a sigh before he grabbed the notes and got back to translating.

~

They got through another three and a half pages of the notes before Sans, hand stiff and vision slightly unfocused from staring at the symbols for so long, suggested they call it quits until Gaster returned; that way, they could just ask about the notes. He had to give it to Alphys—anime was a pretty easy thing to stare at when your brain needed to just stop. Humans were terrible, no doubt, but they had come up with some pretty good ways of killing time; definitely beat out watching a mechanical rectangle dump rose petals on himself for four hours.

They both perked up as the door opened, and Gaster wasn't even in sight before he asked, "You have read through the notes, Sans?" As he entered the room, he was practically buzzing with excitement. "Alphys! I did not expect you here already, but I am glad! We have so much to discuss!"

"Like what this next experiment is?" Sans asked, holding up the first page of notes. Gaster grinned, pulling a crab apple out of his coat pocket.

"Considering you are mobile, I think it is time we tried the machine again."

Alphys fiddled with another page of notes. "A-are you sure? I mean, there's this whole issue of the negative readings..." She scratched her arm awkwardly. "I mean, it could be faulty wiring or something; I did put it together pretty fast..."

"I do not think...well, I can show you. I think you both will find this as intriguing as I do." Gaster's hands were moving so fast he threatened to lob the apple through one of the windows, though he suddenly stopped. "Sans, are you able to walk? I do not want to risk you teleporting into a room outside of time."

"I'm fine.," Sans assured, then shrugged. "I've gone to the kitchen and back a couple times; I'm ready for a marathon at this point, honestly."

"Sans, please be serious."

"I'm always serious." He winked as he got to his feet, lifting his arms and arching his back, getting a few pops from his spine. "Well, that might be a stretch." He waited for a moment, making sure he was balanced, then stuck his hands in his pockets. "Ready whenever you guys are."

Gaster watched him anxiously for a moment, tossing the apple between his hands, then nodded. Alphys got up as well, and the three of them made their way down to the grey room. Sans wasn't doing too bad until the stairs...those weren't fun. As he slowly made his way down, Alphys hovering behind him just in case, Gaster—already at the machine—called, "Alphys, leave the door open!"

"What?" Sans' head shot up to look at the scientist, then back at Alphys as she did just that. "What if someone sees?"

"I would rather have that than risk smoke inhalation if the experiment does not work," Gaster said, tapping at a few of the buttons.

"But we don't have lungs."

"I have lungs!" Alphys interjected. Gaster smiled.

"And a good scientist will always look after a good assistant's health when possible," he said. "Now, both of you, come here."

Alphys waited for Sans to take one last breath, then they both made their way to the machine. Gaster pointed at the screen. As usual, several lines were bouncing at once, but one remained at the bottom of the screen, with no apparent sign of fluctuation.

"You see?" Gaster tapped on the static line. "Over the past few days, it has fallen—gotten 'darker,' so to speak, and it has not risen at all since yesterday."

Sans' browbone furrowed as he leaned in. "But that's impossible."

"It absolutely is," Alphys agreed. "If these readings are negative, then we shouldn't be here. The machine must be broken." She frowned at the screen for a long moment. "Unless..."

Sans looked up at her; Gaster grinned.

"Please, finish your thought."

Alphys puffed out her cheeks. "Unless this is a different timeline?" Her eyes widened. "But that would mean all these lines aren't EM readings for the Underground, but...no..."

Sans' sockets widened as it clicked. "Are all of these different timelines?"

"Yes!" Gaster was practically bouncing. "Well, at least, that is how it would appear. We should have realized ages ago!" He tapped on the screen again. "As we surmised with the study group, a 'reset' moves you along timelines—every decision ever made splinters off into separate timelines, there is an infinite amount of them. For instance, Sans, let us say you started here..." He tapped on one of the lines. "...then you moved here..." He moved his finger down to the next one. "...and then ended up here." He tapped on a third line. "So naturally, when we programmed the machine, we would need to be able to see several timelines." His sockets were bright as he looked at them. "We cannot waste this opportunity any longer! If we can test the machine, we can see where the apple travels to!"

Sans looked at the screen with concern. "What if it ends up in the, uh, dark timeline?"

"Then we can see if that brings any life to that line."

Alphys shifted back and forth. "But...we haven't tested this...I mean, I'm pretty sure it's solid and won't, y'know, blow up, but it's still pretty dangerous."

Gaster laughed giddily, tossing the apple up in the air before catching it. "Then we shall prepare a speech for this brave apple if it does not make it. Sans, check the main controls, make sure the math is correct; Alphys, one last look at the blueprints—if I recall, they are on the workbench, along the wall."

They both nodded, and Sans glanced at Alphys as he headed to the controls. "I've never seen him like this," he whispered. Alphys shook her head.

"Honestly? This is nothing compared to how excited he was when we finally extracted DT." She shrugged. "But I guess that's how he got to be Royal Scientist."

Sans chuckled. "So you freaking out over Mew Mew is practice for when you take over?"

Alphys went bright red, and she gave him a little whack with the blueprint. "Shut up!"

Sans laughed as he turned to the screen, checking the coding. All the equations seemed to be right; still, couldn't be too careful.

He looked up with a small laugh as Gaster, tossing the apple from hand to hand, finally dropped it. "Aw, Gaster, you hurt its peelings."

Gaster shook his head at the awful joke. "One moment, I will get our subject."

Sans returned his focus to the equations, cheekbones lifted; Gaster's enthusiasm was contagious. Just a few more lines to—He jumped as he heard a door slam, then again as there was the clang of bones against metal, and the apple rolled away from the machine.

"Gaster?" he and Alphys called at the same time. The scientist, now blinking from the impact, had stumbled into the main pod of machine. Sans recognized the quick, angry signs his hands made; obviously the fall must have hurt. Gaster took a breath and rubbed his head.

"I am fine, just...er, clumsy; it would appear the apple found me rather than the other way around. Give me a moment to get up."

Both Sans and Alphys gave a sigh of relief.

But then...

...something slithered around Sans' ankle.

It all happened in the span of one second, though it seemed much longer: first was the feeling of his heart dropping to his feet; next was the realization he had felt this somewhere before; finally, his brain worked and he pulled his foot up. But the thing tugged, and suddenly he was falling, and just as suddenly he wasn't, now grimacing as his skull slammed against the console.

"Sans, oh my god! Are you all right?" Alphys quickly pulled him back up.

"Ow...yeah, I do—" Sans was cut-off as the whir of machinery filled the room, followed by a piercing, soul-tearing scream.

He had accidentally turned on the machine.

"GASTER!"

Alphys looked up and let out a scream, while Sans did everything he could to shut off the machine. Nothing worked...why was nothing working? His eye blazed blue as he slammed his fist down onto the console, but it did nothing.

"GASTER!" He gave up on the buttons, and pushed himself away from the console to charge toward the machine. Two claws quickly grabbed him and pulled him back.

"Sans, you can't!" Alphys was just barely able to hold him back, despite the way he struggled against her. Gaster had stopped screaming, but Sans couldn't get the sound of it out of his skull. He kept crying out for the other skeleton, unable to turn away. Gaster's face was caught in an awful grin, and the cracks above and below his eyes spread, growing larger. His hands twitched something incomprehensible as the color faded from him.

"GASTER!"

A massive flash blew through the grey room, and Sans was just barely able to see the scientist melt to the floor. By the time he stopped seeing spots, the machine was smoking, but there was nothing left.

He was gone.

Sans' chest was the tightest it had ever been. No no no NO. He gripped his skull, trying to get any kind of air into him.

He had to write this down.

Without a word, he pushed past Alphys and grabbed a pen. The blueprint was closest. He scrawled out four words, before he could forget.

gaster gone. melted. machine.

"Oh my god!"

Sans whirled around, legs wobbling. Alphys was staring in shock at the machine.

"What the hell happened?"

Sans looked at her in disbelief. "Are you serious?" he asked sharply. Alphys shrank back.

"Wh-what...?" she asked timidly.

"Gaster! He's gone! He's..."

"Erm...who?"

Sans' sockets widened. It was starting. Alphys didn't remember him. Soon he wouldn't either.

"Oh, god."

He quickly turned and looked what he had written. He couldn't forget. He could not forget.

He waited, reading over the four words over and over, every time worried that they would lose their meaning.

But they didn't.

Sans shook, bones rattling. What did this mean? Why didn't he forget?

Was there a chance...?

He quickly ran toward the stairs, nearly stumbling as he did but not stopping. There was no time.

"Sans!" He heard Alphys chase after him. He couldn't stop. He had to get outside for this.

"Sans, stop! What's the matter wi—oh my god!" she cried shrilly as a wave of bones blasted the door from its hinges.

He had to get outside.

No, he had to get to another timeline. One where Gaster had to still exist.

He could survive one more reset.

"Sans, stop, you're not in any state to go out like this!"

He finally stopped for a moment as he stepped into the snow, sucking in Snowdin's icy air and letting it out in shaky breaths. He looked up at Alphys as she stepped out from the grey room.

"Sans, seriously, you're freaking me out," she said nervously, looking at him with concern. He swallowed, then lifted a hand in a small wave.

"I'm sorry. I gotta...I gotta go," he said, voice trembling.

"You aren't making any sense! Where are you—?"

"See ya, Alphys."

"What? Sans, wai—"