"You get it? Huh?! It's funny 'cos marriage is terrible." Stan cackled out loud at his comedic genius as he leant against his convertible, now on his sixth can of (suitably irished) Pitt cola, trying to raise the mood amongst himself, Soos, Wendy and Mayor Cutebiker. It wasn't going too well.

"Maybe we should've joined them." Wendy said as she tried to prevent herself from dozing off in the golf buggy. "It feels pretty weird not knowing what's going on."

"Hey, you heard the kids. They wanted to do this themselves, and we know they can. Who am I to intrude? I'll just slow 'em down."

"I just don't think Pacifica would want Dipper's ex-obsession getting involved in her 'being the hero', that's all. Dude's screwed up enough without some kind of crazy drama."

Soos looked up with a start. "Dude, Paz and Dipper are dating?"

Wendy stared at Soos with a raised eyebrow.

"Are you guys always so casual about this stuff?" Tyler finally asked. "This seems like a pretty weird day."

"Business as usual, slick." Stan shrugged. "Me and Ford have seen stranger than underground market places. Trust me. You don't wanna know what's under Disneyworld."

"Where is your brother?"

Stan shrugged again and took a generous chug of soda. "Distracting himself with video games. The guy's a nerd who's only just discovering the internet. Gotta give him time with this stuff. Besides, the kids can handle these things."

The baffled mayor tried to relax in the strange company he had garnered for the night and bring up more casual lines of conversation. "And how are things with the new family member?"

Stan looked at him and then back at No.13 Geron Street.

"Eh. She's an oddball. Prissy. But she's tryin' to get better and uh… well, I like the kid, y'know? She's good for the family."

"Then what happens after Summer?"

Stan froze. "We've uh… not got a plan yet."

Tyler's moustache bristled. "At all?"

"I thought about her going out to sea with me and Ford but ah… I dunno. She's not like Mabel - Mabel's got that moxy. Pacifica's more…" Stan gestured inarticulately. "...Stay at home."

"So she'd go back to Preston?" Cutebiker asked, sipping the Pitt delicately.

"Over my dead body." Stan snapped back. "The kid's safe with us."

Wendy glanced at the building. "Safe?"

"Damned straight."

It was then that the ground beneath them seemed to shake and quiver - No. 13 beginning to groan and splinter in unison. The relatively unassuming building was now bowing and rolling uncontrollably upon the ground beneath it, trying to stay in one piece as the windows shattered and frames began to cave in upon themselves.

Teal boards snapped away from their frames, screws, nails and joists loosening under the stress of whatever was going on deep inside its foundations.

"...Safe?" Wendy repeated.

"It's uh… it's prolly nothin'."

The road began to crack at their feet. A street lamp fell upon the golf cart, ripping through the awning and landing squarely between Wendy and Cutebiker. No. 11 and 15 split away from the building between them.

"I dunno if that's nothing, Mr. Pines!" Soos shouted, jumping away from the crack that travelled between his legs.

The rumbling grew louder, the street shaking, car alarms kicking off across the street, around the block, on the other side of town …

And then stopped.

"Huh. Mini tremor or something, I guess." Stan shrugged, going back to his drink. "They'll be fine."

Crump!

As if on cue, No.13 Geron street leaned forward - and fell into its own footprint, collapsing into nothing more than a pile of plywood boards and rubble. With it, the doorway seemed to disappear entirely, leaving no trace of that fleshy staircase - indeed, no trace of any real structure behind it at all.

No.13 appeared to be nothing more than an empty shell - and now it wasn't even that .

The group stared at the flat wooden pile that had once been an unassuming entrance to possibly the greatest anomaly in Gravity Falls history.

Stan looked up and grimaced. "Soos, you said you had another way in to this place?"

"I thought you said they'll be fine?" Wendy chimed in.

"They will be. It's the blonde I'm worried about."

Pacifica gripped hold of Dipper firmly, ducking behind him with eyes clenched shut. She had never seen anything so utterly terrifying, so utterly disgusting or so utterly threatening in her life. She was prepared for ghosts by now, prepared for living video games - hell, she was prepared for middle aged men who wore fake tan and tacky business suits - but she was not prepared for a giant millipede demon, especially one that spat acid.

Just looking at those hundreds of legs made her feel itchy and uncomfortable. Bugs were gross at the best of times. This one was fifteen feet wide and slick with smokey mucus that smells like liquorice.

It was just about the worst thing ever .

She glanced at her boyfriend, who said nothing - just stared, with all manner of confusion, bewilderment, awe and outright anger rattling through his head.

Curzon was the Crawlspace . That made more sense than Dipper wanted to admit. He stared up at the creature as it writhed and thrashed against its prospective customers furiously, sending gnomes flying skyward and manotaurs to the floor.

Every building, every tunnel, every chamber in the black market was nothing more than a shell. Nothing more than a ground for it to prey upon and profit from the natural (supernatural?) Inbuilt naivety of Gravity Falls residents and creatures.

All under the bizarre facade of a friendly, cockney market seller who lived in a hole.

Every mouth on the creature's body roared and screamed, spraying corrosive liquid in all directions as the Crawlspace continued to crumble around it - suitably livid at a thousand-year scam being upturned by a few teenagers who should have known better.

If only Grunkle Ford was here. This was beyond crazy. And most irritating was the knowledge that Bill Cipher had known. He had done business down here. If his troops had known, there was no doubt that Bill had.

What had the Pines been missing?! Had this… thing just sat here forever, eating the odd stray gnome or unicorn, sitting under their noses?

It felt personal. He felt personally annoyed . Personally affronted by the fact this… creepy thing had been under his feet for the entire time. For Ford's entire time. Probably before Quentin Trembley's time.

"Dipper!"

How had he been so stupid to miss this-

"DIPPER!"

"Huh?"

Dipper yelped as he was yanked out of the way of a falling slab of concrete by Pacifica, who practically dragged him into a terrace underneath a building marked '42'.

No. 42 would be a charming structure were it not for the skeletal designs carved into every brick and archway. The building was wooden framed, standing resolutely on a series of arches and columns, providing a handy, sheltered catacomb from the world around it.

It was also, unfortunately, filled with barrels of strange green liquids that smelt like sour apples.

It wasn't perfect, but for now, it was as good a hiding place as any.

"Will you stop with the damned daydreaming?! Kinda got a situation here!" Pacifica snapped.

"Look, I… I don't know if I have an answer outside of getting away from here!" Dipper replied, his eyes still broad and his hands clenching his forehead.

Mabel watched the trashing monster and tapped her lip. "I'm pretty sure getting out of here means he'll just hunt us down."

"Mabel's right. I think Curzon probably has good reason to be a little bit annoyed with us."

Curzon's enormous body slammed against the arched bridge that crossed the Crawlspace's plaza, pulling down the building alongside it only metres away from where the kids stood. It was so close that Pacifica still instinctively jumped back from the falling bricks and dust, clinging to her boyfriend tightly.

"And I think he's looking for us, Dipper!" Pacifica yelled, now going beyond basic freakout and into full blown panic. "I'm not up for being crushed by a giant shadow bug, okay?!"

"I'm thinking, I'm thinki-"

What happened next, nobody is really too certain. It's possible it was a case of Curzon striking another of the buildings inside The Crawlspace, in an effort to destroy the teenagers that had outed him.

It's possible that the building fell due to the neighbouring structure suddenly being removed - very abruptly - from its side.

It's also possible that it was due to a Manotaur being thrown by the legs closest to Gertrude, the nature loving old lady, and striking a weight bearing column.

I mean, technically, it's possible that the world above them collapsed of its own accord, but we'll ignore that one.

In any sense, building No.42 of The Crawlspace promptly began falling to the ground - and the floor of the world above was all too eager to follow. What was once a fairly pleasant cobblestone town square was now filled with rubble, dominated by a giant black and blue vaporous 200-legged creature - now, those mountains of rubble were being added to by one of the largest sources of shelter; collapsing directly onto the three teenagers underneath.

Pacifica screamed (and, in hindsight, really wish she hadn't. Embarrassing. ) and ran as fast as she could - before she even had time to realise the twins had stayed still.

The thundering crash seemed to create a deadly silence as Pacifica froze and realised what she'd just done. She stood and stared at the now motionless wreckage that stood in front of her - No Dipper, no Mabel - just piles of concrete, stone and lumber.

She backed up against the wall fearfully and tried her damnedest not to start hyperventilating.

Oh no, oh no, oh nonono-