With the trio now joining them on the footplate, things had gotten particularly tight for space, particularly bizarre and - perhaps worst of all - had completely lost its instinct for planning.

"Tell us what we gotta do!" Mabel said excitedly, detaching the grapple with her foot. "We're here to save the day!"

Pacifica blinked. "I mean, we gotta stop the train and get rid of these things-"

"I'M ON IT!" Grenda replied excitedly, promptly piledriving into the bunker's coal pile fearlessly.

"And we need to stop the train, but the brake uh - broke."

"Broken brakes and evil coal. We've got this! Let's go, team!" Mabel started.

"Wait! This thing's too hot! if it runs out of water, it explodes! If it crashes, it explodes! " Dipper barked, gesturing wildly to illustrate his point. "There's a lot of potential explosions going on, Mabel!"

Candy tapped her lip as she peered at the book in Dipper's hand. "You have the manual?"

"Yeah?"

"I have the toolbox." Candy giggled. "We passed Wendy on the way. She'll be here soon with the Grunkles."

Dipper blinked and looked to his sister.

"Told you I'd keep you guys safe." Mabel replied, sticking out her tongue. "Never underestimate the best twin sister ever! Now let's get shoveling some coalems!"

"We are the Boggl- Huh. Coalems. That's pretty good. Hey guys, how come we never thought of- AUGH" Were the next Boggle's last words as Grenda pounded it into a thin dust.

Mabel was much less dignified in their disposal. She simply scooped a punch of the suckers up in a sack and chucked them over the bunker's side.

"We will be your downfall, humans! There is no escape from the fiery depths of - h, hey, what are you - HEY!"

"Sayonara, suckers! Boop!" She beamed as it flew overboard, landing in the middle of the forest clearing that had been their sleepover spot only a couple of days prior.

To Dipper's surprise, Pacifica, Grenda and Mabel were more than capable of putting a rather obvious dent in the Boggle pile. Their numbers were depleting rapidly - making it substantially easier for him to work with Candy to try and repair that brake lever.

"Type six pin goes here and we take these teeth out of the rods…" Candy mumbled intently, while dusting off the remains of the Boggle with a brush.

"Can't we hurry it up?"

"You can't rush art, Dipper." Candy scolded. "There's much at stake if we make mistakes."

"There's more at stake if we hit another train!"

"You always worry too much." Candy replied, grabbing a mallet from the toolbox and whacking in the new lever pin with a smug smile. "Pull."

Dipper did as he was told - though not without being a little irked by Candy's seemingly unshakeable demeanour. The lever moved - stiffly, but moved all the same, and began to resist as the brakes bit into the wheels.

The wheels locked. A hideous, piercing, screeching tone erupted from tires. Sparks flew in brilliant golds and oranges. The entire thing was now skating - they had only succeeded in losing more control over the enormous lump of machinery. To make matters worse, the lever was rattling like crazy; as if it was about to burst out of its casing any second.

"We aren't slowing down!" Dipper yelled. "Can't we do something else?!"

Pacifica grabbed the handrail and winced. "I can't hear you?!"

"We need someone with more than just Vikipedia experience!" Candy grunted, sliding the brake back off. It snapped back so resolutely it lifted her off of the floor. Their speech became audible to one another again, mercifully. "Why don't they teach us to drive trains in schools?!"

"THAT'S A DUMB IDEA, CANDY."

"You cannot call the idea dumb when it would help!"

"CANDY, I SWEAR, SOMETIMES YOU MAKE ABSOLUTELY NO SENSE!" Grenda roared, as she shovelled another 30 kilo pile of Boggle over the side of the locomotive's bunker as if they weighed the same as a candy wrapper. "WHY DON'T YOU JUST MAKE SENSE?!"

"Guys, guys, don't let the tension get to you!" Pacifica snapped. "Calm down! We're not gonna die or something!"

"Oh my god," Mabel whispered. "You think we're going to die?"

"WE'RE GOING TO DIE?" Grenda yelled with the next comically outsized shovelful of screaming, foaming coal gremlins.

Pacifica held her forehead as the panic began to set in.

Mabel ran over to the controls and reached for as many levers as she could. "What do we do, what do we do?!"

"I don't know!" Dipper yelled. "Mabel, don't-"

Mabel pulled a handle and sand began to fall onto the rails, to help the wheels grip. She looked to the others urgently, paying little heed to the fact the engine was now even noiser . "Can't this thing go backwards?"

Dipper and Pacifica opened their mouths to reply, dumbfounded by the rather basic - albeit temporary - solution, as the locomotive screamed forward. At least if it was going backwards it wasn't flying towards the real railroad with multi-thousand-ton trains and passengers.

"Well, which one makes it go backwards?"

Dipper grabbed the manual and desperately shuffled through. "I- I dunno, I-"

"I'm gonna bet it's this one with 'F' and 'R' written on it." Mabel replied, somewhat dismissive to the group's larger concerns. She grabbed the lever and excitedly rammed it back before the others could protest.

Mabel's guesstimate was a decent enough one, sure - but this bizarre huffing dragon of a machine was like something from another world. The kids couldn't be sure what was a right move, what was a wrong move, or what would cause the thing to blow up like a bottle of Pitt with Ventos in it.

Then, something shifted. They couldn't quite explain how - but they all felt it. Something was different. Rods and levers clanked on the locomotive, and it seemed to… jolt.

Explosive exhaust became faster-paced; wheels screeched. A marked, hollow, bellowing hiss began to develop from number 4.5's front, and, to the Pines' surprise, she lost momentum. The hissing, wheezing machine finally paused with an abrupt rattle - but only momentarily.

Then, slowly at first, the rattling, fire-breathing rocket began running backwards.

"Hit the brake! Hit the brake!"

Candy nodded and pushed it, only for the entire mechanism to resist her. The petite Korean girl's feet simply slid against the floor as she tried to put her entire weight into it. "I- I can't!"

"What?! Come on, Candy, we gotta!" Dipper yelled back, shoving it with her. Mabel joined in, as did Pacifica, all struggling to stop the engine before it was going too quickly. It was perhaps endemic of their modern trust for technology that they overestimated the strength of the rods, levers and bars that were meant to stop the forty-ton runaway.

"I'LL HELP!" Grenda boomed, pushing it with them while deflecting a Boggle. Thanks to the girl's unwieldy (some might say catastrophic) strength, it pushed forward a notch. And another. And another.

The screaming erupted again. They thought they could smell burning from the wheels underneath them. They pushed and pushed, as the natural forces of the great metal beast pushed back, grunting furiously like a bull being caged.

The creaking noise grew, and grew, the stalemate growing more and more desperate, when - with a final groan, something split. Something bent. Something snapped. The lever fell slack, and as quickly as they had managed to scavenge some hope, they had lost it - and were officially brakeless. The remains of the mechanism, on the outside of the engine, fell to the rails and was mangled underneath, left behind in a pile of unkempt rods, hinges and bars. The kids fell painfully to the floor in a heap alongside the now useless lever, as the engine continued steaming backwards, unabated.

Pacifica held up the sagging lever and winced. Her shaking, snow-white hand took Dipper's as she fearfully looked in his eyes. For once, it seemed like nobody had any answers. They were truly out of control - truly trapped.

The locomotive roared victoriously as it continued reversing at full pelt. The wind that flooded into the cab was bitterly cold and whistled through the wooden cladding, the clattering wheels bucking and bouncing over the slightest joint in the rails. They may have avoided a potential collision - nobody was doubting that - but the thing felt far less stable when running backwards. They felt far more exposed.

The relatively insignificant Boggle pile continued its furious assault while the kids were down. While they may not have had the fire to target, they had plenty of vulnerable looking locomotive controls to throw themselves against, and that was close enough. To make matters even easier, they now had the wind behind them - and that kind of air turbulence only made them a more volatile projectile. The kids stayed down onto the floor, yelping as gauges were smashed, windows shattered, bolts kicked loose and pipes dented, the locomotive only growing faster and faster as the overheated fire continued to roar furiously.

The dichotomy in the engine's behaviour was clear. A force of nature, certainly - but having only just been put back together from a giant mechanical jigsaw puzzle, the maiden trip had become little more than an aggressive hammering. She was beginning to leak steam, rattling more than ever - as if every inch of her framework was struggling desperately against the immense pressures she was being subject to. The thought never occurred to the kids - but if things kept going as they were, even if, by some miracle, they managed to stop, there might not even be an engine left at the end of it to run the railroad.

To the young group aboard, it seemed unthinkable. By rights, such a machine - to them - seemed like a practically impervious fortress, towering over and around them, made of iron, steel and oak. But time was running out, and every beat of those thundering pistons only brought them closer to ruin.

Should that unthinkable happen, there really would be no escape. And the Gravity Falls railroad would collapse with it. The end of a beautiful, albeit slightly faulty dream of the little place in Oregon where time and progress seemed to stand still…