Jemma peeked through the curtain, scanning the crowd beyond.  Dozens of humans and monsters filled the rows of seats, but the one monster she was looking for wasn't there.

"Jem.  Like, what are you doing?" Bratty asked.

"Bratty, she's totally looking for Sans," Catty replied as Jemma let the curtain fall back into place.

"Sans?" Bratty asked.

"He promised he'd be here, since he's leaving tomorrow with Papyrus and Frisk," Jemma explained.

"Did he ever tell you what he wanted to?" Catty asked.  "All he told me was to find you and send you in the direction of the lounge."

"Oh, is that what you were talking about yesterday, Catty?" Bratty asked.  "I thought you were telling her about Mettaton."

"No, I don't ship Mettaton and Jem!  Yuck!  I like, totally ship Jem and Sans."

"Darling, come on!" Mettaton said, appearing from around the other side of the curtain.  "The show is starting!"

He grabbed Jemma's arm, pulling her away from Bratty and Catty and out into the bright stage lights.  The crowd cheered, the deafening noise crashing into Jemma's ears.  She stood rooted to the spot.  In front of her was a sea of unfamiliar faces, and for the first time Jemma felt a twinge of doubt.  Where was Sans?  He had said he would be there.

Then the music started, and Jemma pushed aside her doubts and fears.  So Sans didn't come.  That didn't mean anything.  So what if they had gone to Grillby's together last night, just the two of them?  So what of he was there before every show, without fail?

Jemma started singing, letting herself be swept up in the words.  Moments later Mettaton joined in, harmonizing beautifully with her.  The performance went perfectly, just as they had rehearsed.  They sang song after song, filling the room with energy.  As Jemma started into the final song her eyes were drawn to the back door as it swung open.  Sans stepped through, ragged and slightly hunched.  One of his eyes was glowing a steady blue.  Jemma stumbled over her words, missing several notes.  Mettaton's voice steadied hers as the song ended.  The curtains closed as the crowd roared it's approval.

"Great job, darling," Mettaton said.  "But what happened at the end?  I've never seen you-"

"Sans!" Jemma interrupted.  "I've got to find Sans!"

"Darling, wait!" Mettaton called.  But Jemma had already vanished backstage.  She rushed down the hall, nearly colliding with Sans as he turned a corner.  His eyes were back to normal, but his hoodie was ripped in several places and smudged with dirt.  He grinned faintly.

"You in some kind of hurry?" he asked.

"What happened?" Jemma responded.  "When you came in your eye was glowing blue, and you looked like you were hurt-"

"I'm fine," he interrupted.  "But Jemma, I have something I need to ask you.  I hate having people make promises, and it's going to be very dangerous, and I know you're about to have your childhood dream fulfilled, but you might be the only person who can help me."

"Why?  What happened?"

"They took Frisk and Papyrus.  I tried to stop them, but they didn't fight fair.  It was a hit and run.  I barely escaped capture.  I think they were only after Frisk, which is why they didn't put up more of a fight with me.  I think I know where they are, but I need someone else to come with me.  Someone to watch my back."

"Who took them?" Jemma asked, heart pounding.  Sans' eyes dimmed.

"Gaster's followers," he growled.  "I don't think they knew who I was, or they wouldn't have let me escape."

"Gaster?  As in Doctor W. D. Gaster, the scientist you worked for?"

"That's the one.  I can't let the trail get to cold.  If you come, I'll explain things on the way to the Underground.  Otherwise, I'll see you if I make it back."

Jemma hesitated.  Leaving would mean missing out on her chance to become a famous singer.  Who knew how long it would be until Mettaton came back from his travels?  But on the other hand Frisk and Papyrus were in danger.  And Sans needed someone to help him.  Someone he could trust.

"I'm ready.  Let's go," Jemma told Sans.  He smiled.

"I knew I could count on you," he said.  They walked together down the hall, to the hotel's back door.  Outside in was dark, but heavy clouds blotted out the starlight.

"Most of the monsters stayed in the Underground, and we haven't had any humans visitors since Frisk," Sans explained.  "So you'll stick out a lot, but we don't have time for a disguise.  Besides, Gaster's Followers won't recognize you."

"Tell me about these Gaster Followers," Jemma invited.

"It's a long story," Sans sighed.  "Gaster was put in charge of finding a way to extract the human SOULs and use them to break the barrier that held us trapped.  Well, after the first human was killed and their SOUL extracted, it took a long time for the next to come.  So Gaster started experimenting with the SOUL.  He wanted to know what it was that let it exist after death in another timeline.  He made a machine which let him travel between timelines by injecting himself with human determination.

"Well, long story short, Gaster went mad.  He went to other timelines, killing monsters just to find out what would happen.  Just so he would have more test subjects for his experiments.  After all, they weren't our timeline.  With the help of the sixth human, I defeated Gaster and broke his machine.  He was shattered across the different timelines, bits of him going into different people and places.  I have a piece of him, which is how I can see LOVE and EXP.  His followers have the other pieces."

"How did they get the pieces of Gaster if they're in different timelines?" Jemma asked, struggling to wrap her head around the idea.

"They fixed Gaster's machine and injected themselves with determination, making them more powerful than regular monsters," Sans answered.  "They want to resurrect Gaster, but they can't do that.  They don't understand that Gaster would kill them in a heartbeat.  Sure, first he would destroy all of the humans.  But when they ran out, he would turn on monsters.  Oh, and they hate me because of what I did to Gaster."

"Why would they need Frisk?" Jemma asked.  Sans was leading her to the outskirts of the town, towards the base of Mt. Ebott.

"Since Gaster shattered, so did his SOUL," he explained.  "The only thing keeping him alive is the determination he injected himself with.  That means he needs a new SOUL if he wants to be completely whole.  I'm sure his followers thought it would be perfect to get him Frisk's SOUL, considering she's the eigth human to enter the Underground."

"Eight?  I thought there were only seven."

"Seventh.  I meant to say seventh."

Sans glanced away, scanning the trees around them.  Jemma could tell that he was hiding something, but she decided not to press it.  There would be time later to find out the truth.

"One last thing," she said.  "How could you take the soul of one creature and give it to another?"

"I forgot that humans don't know what SOULs are either," Sans sighed.  He stopped walking under the shadow of the trees.  He turned to Jemma.  One of his eyes glowed a bright blue, casting devilish highlights over his features.  Jemma felt a tugging in her chest.  A silver heart appeared in the air, hovering mere inches in front of her.

"That's your SOUL," Sans explained, a pained look in his eye.  "I've never seen a human SOUL that looks that much like a monster SOUL.  Anyway, when a monster dies their SOUL shatters and their body turns to dust.  When a human dies, their SOUL becomes separated from their body and . . . well, we don't really know what happens then.  I think they're sort of recycled, used in another human body.  Something about the determination gives them another chance at life."

Sans' eye lost it's glow and the silver SOUL returned to Jemma's chest.  They began walking up a thin trail which wound up the mountain.

"Sans, why can't I see your LOVE and EXP?" Jemma asked after a moment.

"Why would you want to?" Sans replied.

"I was just wondering, since I can see everybody else's.  But whenever I look for yours, it turns hazy and vanishes."

"They're just numbers," he said quietly.  "LOVE and EXP don't say reasons."  He paused, listening as the leaves crunched underfoot.  He sighed.  "If you're about to die, I'll show you my LOVE and EXP.  But only then.  And I'll be the judge of if you're about to die."

"Promise?" Jemma asked, more for the sake of conversation than because she actually wanted a commitment.  Sans hesitated.  Jemma was about to reassure him that he didn't have to when Sans interrupted her.

"I promise."

They halted at the edge of a cave.  The musty breeze coming from inside smelled of mildew and, if it was possible, brimstone.

"Welcome to the Underground entrance," Sans announced.