Much as the locomotive's excursion into the corkscrew tunnel had been a painfully tedious one, the crew of the Northwest Speeder had rapidly lost interest in their perilous situation. It was like a bottomless pit, but with the clickety-clack of rail joints and the putter-patter of a life-expired petrol motor. And a mild amount of motion sickness.

"Gosh, this sure is a loooong tunnel." Susan said, even her usual chipper tone beginning to take on a feeling of fatigue.

"Candy is ready to sleep now." The most diminutive member of the group agreed.

"Well shucks, y'ain't gotta wait so long!" McGucket chirped, applying the speeder's handbrake. "Sure am glad the rails ain't wet or nuthin'!"

"BUT THE RAILS ARE WET!"

"Yup, shure do feel good to be on good, dry tracks!"

"But the rails are-"

"Shure am glad to be in good company on good, dry railroad!"

"But the raaaails aaaare-"

The speeder was a torquey, fast-faced little blighter when it so desired to be - especially on a highly unrealistic helix gradient that rode like a sort of steel-asphalt NASCAR. All the same, there was no getting around the fact it was based upon a terribly engineered mess of a late-30s British motor that was put together by a drunken man called Errol at 4:45PM on a Friday.

The brakes were nothing more than a single bar-lever, much like the locomotive that had come before it. It also weighed practically nothing. A combination of those factors meant that the wheels just… locked. Each wheel stopped spinning and skated down the shallow hill into the water-hall with a high-pitched squeal, trailing a thick layer of orange sparks behind them.

"Well shucks, mah handbrake ain't workin. Why didn't anyone tell me that th'goshdurn rails were wet?!"

Exhaust flew as McGucket tried to put it hard into reverse, only increasing the loud complaints from the ancient Royston motor. Squealing, gurgling and hissing, water sprayed from the overtaxed radiator.

Pacifica and Stan both ran into the tunnel, puffing and panting, and began waving desperately at the vehicle as it roared down. They only became more concerned when they realised that Candy and Grenda were aboard.

"Stop! Stop!" The Northwest heir shouted, waving her arms."Oh nonono, what are they doing here?!

Stan joined into the refrain. "McGucket, ya gotta brake this thing!"

"Well hey, it looks like we got a welcome party!" Fiddleford replied excitedly, as if he wasn't currently on a sprinting projectile. "Howdy there!"

McGucket tried again to force the vehicle in reverse, thick black clag erupting from the vehicle's chrome exhausts in fierce bursts that threatened to singe Lazy Susan's hair. The vehicle rattled uncomfortably, and then...

Crunch!

Fiddleford's face fell as he held up the stickshift, now attached to what was left of his gearbox. No longer restrained by its gearing - and no longer physically capable of being put in reverse - every ounce of the vehicle's weight dragged it down faster still.

"Well dang."

"Oh my gooosh! We're going to craaash!" Susan yelled, gripping her seat.

"C-candy is scared now!"

"I NEVER LEARNT HOW CARS WORK AND NOW I'M SCARED TO ASK!" Grenda chimed in.

With an ear-piercing, endless screech, the smoking, battered motor continued its steep glide down towards Stan and his adopted great-niece. They took a step back, still desperately waving, still trying to communicate an impossible task to the crew of the rapidly approaching speeder.

"W-what are we gonna do?!" Said adopted great-niece asked, frantically.

Stan winced. "Get outta the way, Blondie."

Pacifica looked up at the old man and raised an eyebrow. "Wha?"

"I said get outta the way."

Pacifica backed away slowly. "W-what are you gonna-"

"Get outta the way! Scram!" Stan barked.

Pacifica's eyes widened and she dodged back into the water hall, while Stanley steeled himself and, as soon as the vehicle was closing the distance on him, lept aboard. In his mind, it was probably meant to be a heroic moment. In reality, he fell face first into the footwell, perched precariously over a red-hot engine hood that threatened to burn out his appendix faster than his homemade moonshine.

"Stanley?!" Susan gasped, helping him up. "What are you doing?! You could hurt!"

"Can't leave you alone, sweets." Stan winked. "Besides, if there's one thing I know, it's how to force a car engine ta do what I want."

The old man ripped out the dashboard and threw it behind them. He stuck his hands into the mess of tangled wiring. "You guys might've hearda hot wiring, but in the 80s, I kicked off a trend of cold wiring. Learnt how ta mess up a car so badly that it bricks itself and makes it look like th'factory's fault. Insurance scam earned me twenty thou'."

"What happened…?" Candy ventured, raising an eyebrow.

"Drinks at the Holy Mackerel lodge. Freakin' expensive."

The old man did something alright. With a dull 'fzzt' and a hissing noise, the Speeder sagged slightly on its suspension and stopped spitting out exhaust fumes. It slowed ever so slightly, the seized wheels beginning to turn again and, finally, beginning to slow.

Pacifica stared in awe as the vehicle silently rolled past her, into the water-hall and, finally, came to a stop just before striking the wreckage. Dipper, Mabel, Trembley, Ford, Dan, Kevin and Gus all peeked through the hole and over the mass of twisted iron with surprise.

Finally, it bumped lamely into the overturned tender, and came to a halt with a comically minor 'ding'.

Fiddleford blinked, still holding his steering wheel. Candy and Grenda lept off and cheered as if they'd just survived the world's longest, most tedious rollercoaster.

And Susan simply stared into Stan's eyes with a smile.

"Well done, Stanley." Ford beamed, slapping Stan across the back.

Stan, ever-proud to receive a compliment from his brother, saved it off with a smile. "It was nothin'. Can someone peel me offa this thing? This cheap poly suit has melted and I think I've got a third-degree burn."

Trembley brought out his emergency government-mandated fish slice, while the little reunion took place. Handshakes, hugs, and the occasional back-crack from Grenda's famous vice-grip were exchanged while Dan peered over at the wrecked locomotive and battered Speeder and considered raiding them both for parts.

Ford beamed as he held McGucket's shoulder with unmistakable fondness. "We really appreciate you all coming to help, but honestly, it seems like the worst of it is over."

"We missed fighting?" Candy huffed. "I was ready to kick monster butt!"

"WELL THEN NOW WHAT?" Grenda added, hands on her hips. "WE CAN'T JUST STAND AROUND TALKING!"

Dipper then blinked as he held Pacifica's waist. "H-hey. Can you hear that?"

Pacifica held her hand behind her ear and strained. "Yeah. It's like a-"

"Earthquake?" Mabel ventured.

Ford held his chin and pulled out his patented homemade pocket seismograph. "Not impossible, but it'd be a damned bizarre coincidence…"

Unbeknownst to the foolhardy gathering of townsfolk, the valley itself was beginning to react to the day's terrible events. Every inch of the rail ties and foundation spikes glowed white hot as the energy built within them, tearing into the clay and stone of the town's surroundings. It continued to dive deep into the earth, ripping into a terrine of terranes and sediments.

The crack travelled downwards with a fierce urgency, slowly widening and stretching the railroad ties until each metal rail popped free from its mounting. Across the sleepy little town, a vibration was felt, flood water splashing back and forth and rippling against every structure.

To the horror of the crew in that cavernous hall of water tankers, the room began to shake, and crevices began to open up between the ancient flagstones. Rails slumped, and the crew struggled to remain on their feet as the subterranean catastrophe unfolded.

Widening foot by foot, they soon stood on a six-foot-wide slither of concrete and earth, while around them, switches sank underground, spilling each of the water-filled wagons forth into the great depths of the Earth.

They stared in awe, occasionally gasping and yelling in surprise as the world seemed to unfold itself. The room above them began to rattle and shake, ancient concrete and cinder-block reawakened by the sudden shifts in the earth they had been cossetted by for over a century.

"That's not good." Ford winced, peering down the crevice.

"What?" Kevin chimed in. "It's just a hole, right?"

"You've all noticed that blue foliage we keep seeing underground. You can guarantee there's plenty under there. If that stems from the same extraterrestrial stuff as everything else we've come up against…"

"The lake water." Dipper interrupted. "It'll go nuts."

"It'll no doubt mutate." Ford groaned, holding the bridge of his nose.

Pacifica clung to Dipper tightly. "So…so what does that mean?"

"If it's the same glowing blue crap we've seen all year, I gotta be honest, I'm worried. That crap's strong. It's like ragweed. Pushes through just about everyth-"

Stan was rudely interrupted by the cracking of stone, deep down in the chasm. An all-too-familiar, ethereal glow began to seep from the darkness, more of the water tankers falling into the seemingly endless fault lines that wrapped around them.

"Kids, here may not remain here for much longer. It could affect the structural integrity of the entire town." Ford said, in a matter-of-fact manner that almost obscured the severity of the situation. "We could be facing a full structural collapse."

"Great. We're gonna be mole people." Pacifica groaned.

"Ah've met mole people an' they all smell like refried beans!" McGucket guffawed, as if being threatened with subterranean living was just part of his day-to-day. Though he was a government contractor. It probably wasn't that unlikely.

How much of Gravity Falls' beguiling blue essence was pouring into the earth? How much of a hazard could it really offer? The idea of that familiar blue foliage going into overdrive didn't - on the face of it - seem so sinister. But knowing that the town hung in the balance, knowing that the integrity of the Northwest manor was becoming so precarious - knowing that all of this had the potential

And then, they felt a jolt.

The Pines yelped and tried to clamber back onto the relatively solid ground of the complex as their sliver of concrete rose like an elevator. With only moments to spare, before it pounded against the ceiling above and brought done a clod of stonework. Tendrils of rapidly flowing blue ferns followed this, each one illuminated in that horrible aqua that had haunted them so consistently this summer.

Pillars of earth rose, one by one like giant pencils, pounding into the fragile ceilings and foundations of Northwest Manor above, and began to pierce it. Across the entirety of that dark chasm, surrounding the town, the very foundations of Gravity Falls were beginning to sink and crumble, every underground tunnel and burrow dug by Cankerblight beginning to rattle and shake, as blue vegetation began to sprout from every crack, crevice and crease in the Earth's fabric.

Nathaniel Northwest's ultimate plan was coming into action - and the only man who had seen the blueprints for it all was tied up on the roof of the courthouse.