The cave held a winding stairwell which spiraled deep into the earth.  As Sans and Jemma descended, the only sound was their footsteps on stone.

"Stay close," Sans warned.  "As long as people see you're with me, they'll leave you alone."

The tunnel widened into an enormous cavern.  Sans and Jemma stood on a raised outcropping which offered a view of the entire Underground.  Below them stretched the Capital with the castle nestled among its buildings.  Beyond the Capital was a lake of glowing blue liquid.  A dark waterfall cascaded from the ceiling, reflecting the glittering lights from the cavern roof as it bled into a river which trickled out of sight.  In the distance a large machine jutted out from a pool of lava, geysers of hot air erupting around it.  A snow-filled forest of skeletal trees filled the farthest corner of the cavern.

"That's where Papyrus and I used to live," Sans said, pointing towards a small village nestled in the snowy woods.

"It's beautiful down here," Jemma agreed, glancing up at the sparkling roof.

Sans continued down the rest of the stairs, glancing back to make sure Jemma was following.  They crossed the streets of the Capital, drawing eyes from the various monsters which lived there.  Jemma found herself moving closer to Sans as monsters appeared in the shadows between buildings, watching their slow progression.

"This way," Sans said, sidestepping into an empty alleyway.  "I know a shortcut."

"Where are we going?" Jemma asked as the shadows darkened.

"The original Grillby's.  Grillby works there during the day.  At night his daughter Fuku Fire runs the place.  We go back pretty far.  Chances are she'll be able to point us in the right direction."

Jemma felt a momentary stab of jealousy.  She pushed it away and hurried to catch up to Sans.  There was no reason to be jealous.  Fuku was going to help them.  She wasn't competition or anything like that.

When the shadows brightened again, Jemma and Sans were standing in front of a glowing restaurant, snow crunching ynder their feet.  The glowing neon sign proudly labeled the building Grillby's.

"After you," Sans offered, pulling open the door.  Jemma stepped inside as warm air that smelled like burgers and french fries enveloped her.  The interior of Grillby's was well lit, a near perfect copy of Grillby's Place on the surface.  The only difference was that Grillby's was smaller and, at the moment, empty.  A girl made of green fire was behind the counter, twirling a glass absentmindedly.  She sat up as Sans closed the door behind them.

"Sans, how are you?" the girl asked.  "I haven't seen you in forever!"

"Doing good, Fuku," Sans replied.  "How're you?"

"Bored," she sighed.  "But looks like things are about to get interesting."

"Fuku, this is Jemma.  Jemma, this is Fuku."

"I'd shake your hand, but . . ."  Fuku shrugged.  As she stepped out from behind the counter, Jemma felt another prick of jealousy.

Fuku was the prettiest monster Jemma had seen so far, aside from Undyne and Mettaton.  But Mettaton didn't count, and Undyne was more of a dangerous kind of pretty.  Fuku was dressed in a skirt and white blouse, a school uniform of some kind.  Her only facial features were her eyes.

"What can I do for you?" Fuku asked.

"Since you're the smartest monster I know, I was kind of hoping you could help us," Sans replied.

"Sans, stop it," Fuku protested.  Her cheeks had began emitting sparks.  "I'm street smart, not brainy."

"And that's what we need," he said.  "Jemma and I are on the trail of Gaster's followers.  Any idea where their hideout is?"

"Don't mix up with Ghastlies," Fuku warned.  "They're crazy.  Why would you want to?"

"They kidnapped Frisk and Papyrus."

"That cute little human?"

"That's the one.  Heard anything?"

Fuku tilted her head thoughtfully, burning brighter for a moment.

"They're trying to reform Gaster," she guessed.  Sans shrugged.  "Well, you don't have to worry.  They're three pieces short from making him whole.  Rumor is they're going for one of the pieces tomorrow.  Something about the True Lab?  No idea where that is, but that's where they said the piece is."

"Thanks a million, Fuku," Sans said.  "You really saved my skin.  If I had any, that is."

"Come again!" she called as Jemma and Sans left, closing the door behind them.

"Do you know where the True Lab is?" Jemma asked.

"Yeah, I do," Sans replied.  He glanced at Jemma.  "But we'll go there tomorrow."

"Why not right now?  Frisk and Papyrus need us!"

"Because they'll be ok for a bit, and we can't even get to them until Gaster's Followers go to the True Lab.  Besides, you look exhausted.  And I'd like to change into a new sweater that isn't ripped."

Jemma had a protest ready, but she realized that Sans was right.  She was exhausted.

"You can crash at my place," Sans offered.  "While you do that, I'm going to go scout out the lab.  I'll come get you in an hour or two."

"But no later," Jemma warned.

"Only an hour or two," Sans agreed as they walked down the snowy street.  They stopped in front of a two story log cabin.

"The door's never locked, so you can just go in," Sans explained.  "I'd recommend the couch in the living room.  It's surprisingly comfy.  Even Undyne says so."

"One hour," Jemma repeated as she opened the door.  By the time she looked back, Sans was gone.