Warning: There will be death, swearing, and slight body horror in this and the following chapters. Proceed at your own risk.

Disclaimer: Any characters or objects from Gravity Falls and/or Supernatural do not belong to me, and I am in no way making any profit with this story.

"Mabel! He's coming!" The tattered old knapsack was dragged out of the closet.

"But-but what about Mom and Dad?" In went a fleece and a crumpled wad of five dollar bills.

Dipper hurriedly grabbed a knife from his chest of drawers and threw it into his backpack. "He's not after them, Mabel! He's after us, and we have to go. Now."

Two pairs of socks. A change of underwear for each of them. A road map of the U.S. Mabel set her jaw. "I'm not just going to leave them."

Dipper stuffed a worn leather pouch into the backpack before turning and grabbing her by the shoulders. "Mabel, we have to run! He's gonna -" There was a crash below them. Dipper paled. "He-he's here."

He grabbed another pen knife from the shelf and tossed it to Mabel wordlessly. She caught it by the handle, fumbling with it a bit as she flipped it open.

An echoing voice drifted up the stairs, dripping with gleeful malice. "Oh, children..."

Mabel went white. "Oh, God," she whispered. Dipper had already made it halfway out the window, but she was rooted to the spot.

Dipper paused and set his backpack down on the fire escape. "Mabel! Come on!" He whispered. Mabel shook her head, trying not to hyperventilate. Then she had an idea. She unfroze and grabbed a sharpie from under her bed. She could panic later.

"J-Just a sec, bro-bro."

The stairs creaked behind her. "Tell me I'm getting warmer... You two have been just begging to be turned into corpses for ages."

Dipper's eyes were saucers, but he didn't run. "Mabel!" His voice came out squeaky and panicked.

"Just a sec! Go, I'll catch up!" Mabel continued scrawling on the wall as fast as she could. She tried to keep the tremor out of her voice.

"I'm not leaving you!"

She could hear him in the hallway now, padding across the carpet, steps slow and deliberate. The lamp in the corner of the room flickered with each footfall, electricity arcing across the wires with a clinical regularity. Just a few more seconds... And...

"Done!" Mabel threw the sharpie to the ground.

"Great! Now, come on!" Dipper grabbed the edge of the ladder and started to lower it down. Too late.

Behind them, the door to their room creaked open. An eerie glow lit up the room, reflecting off the whites of Dipper's eyes, turning them an unearthly green. She felt a tingle on the back of her neck.

"M-Mabel! Behind you!" Dipper shouted, his voice cracking.

She whipped around. The light from his eyes threw most of his face into shadow, obscured his features, but she didn't double-check to see who it was. She didn't need to. The slitted pupils of his awful eyes, that snakelike grin — those were enough for her. As he took another step towards them, her hands stopped shaking. Her eyes narrowed involuntarily. She could panic later. Right now, she had to move.

"Eat iron, butt-face!" She threw the penknife. It wasn't nearly the same as her old grappling hook — and she'd never had the best aim to begin with — but it was good enough. Hitting him square in the arm, it made a sharp hiss as it made contact, flooding the room with the smell of burnt turkey. But the man with the awful eyes simply looked down and laughed.

He yanked it out and twirled it between his fingers. "Iron blade. Somehow, I expected more from you. I mean, seriously? Did you really think that a little thing like iron would work on -" He looked up and stopped.

The window was open, the white curtains flapping in a nonexistent breeze, lit up by the otherworldly glow. The fire escape was empty. The twins were gone.

The man's face darkened and his eyes flared yellow. A blue flame curled around his clenched fist. "I said I would kill two humans named 'Pines' today." He stepped out into the hallway. "But I'm not too picky about which ones."

There was a sizzling sound, and a thick cloud of smoke drifted into the twins' bedroom. There were two simultaneous screams. And then there was silence. The man was gone. And two burnt and blackened corpses lay where the twins' parents used to be.

Sam looked up from his newspaper. "Dean, get this: 'San Francisco couple slaughtered in their beds.'"

Dean chewed his pancake. He didn't look up. "And?"

"It could be a case, Dean. Our kind of case, I mean."

"Or it could just be a regular murder. Those happen too, you know."

"We've run with less before."

Dean put his fork down. "All I'm saying is we should probably be focusing on stopping Lucifer. You know, keeping the seals from breaking? Stopping the apocalypse? Ring any bells?"

"And I'm not saying we shouldn't." Sam said hastily. He set his newspaper down on the checkered tablecloth. "But we have no idea which seals are going to be broken next. So, it's a little difficult to be actively trying to stop the apocalypse when we don't have anything to work with. So, I thought - since we've got nothing - it couldn't hurt to look into this."

Dean paused, then shrugged and wiped his mouth. "Fine." Then he fixed Sam with a glare. "But if we get word that another seal's going down, we go stop it. No questions asked. I'm all for saving people, but I'm not just gonna sit back and watch as the freaking apocalypse goes down."

Sam hid a smile and stood up. He glanced at the keys in Dean's hand. "Can I drive?"

Dean snorted. "In your dreams."

The forensic pathologist raised an eyebrow at Sam's badge. "FBI, huh? I figured they'd get you guys involved. This was a weird one."

"How so?"

The man shot him a look and pulled the body out of the freezer. "Didn't you read my report?"

Sam tensed, but replied smoothly. "I know the basics, but I'd still like to hear the details. From the source, I mean."

The man huffed and twitched back the plastic. "See for yourself."

The corpse was a woman, though Sam probably wouldn't have known it if he hadn't asked to see her specifically. Her flesh had charred and blackened beyond all recognition, her lips shriveled and scorched to reveal burnt-black gums and brittle teeth. And from the hollowness beneath her eyelids, Sam could guess that her eyeballs had melted from the heat of the flames.

"We've got no idea where the fire started, and any fingerprints that were there to begin with have pretty much burned away. There's gonna be an autopsy later, but don't get your hopes up. They're basically charcoal at this point."

Sam leaned in closer and lifted up her eyelid. It crumbled away in his fingers, leaving behind an empty socket. He swallowed and made a face.

The man nodded. "Nasty, right? Poor schmuck's husband looks the same."

"Jesus." Sam muttered. Then, a bit louder, he asked, "Any idea who did it? Anybody who'd maybe hold a grudge against the Pines family?"

The man shrugged and zipped the body bag back up. "Hell if I know. It's a big city, I never met 'em. You're the fed, you figure it out." Then he seemed to reconsider. He lowered his voice. "But between us? My money's on the kids."

Sam raised his eyebrows. "The kids? Why?"

"'Cause the doors were locked from the inside, and these two didn't die in a freaking house fire. They were found like this in their beds. And when we found them, their kids had already skipped town."

Now they were getting somewhere. "Any idea where they'd go?"

"Dunno. Up and vanished. Afraid of getting caught if you ask me."

"Huh."

"Yeah. It's really screwed up." The man paused, then pushed the woman's corpse back into the freezer. He brushed off his hands. "Do you need to see the husband?"

"No." Sam straightened up. "I think I have enough for now. Thank you for your time." He turned to go, then stopped and looked over his shoulder. "If you find anything strange in the autopsy - anything at all, call me."

"Will do." The man turned away. Sam left the room, pulling his phone out of his pocket as he stepped through the door.

"Hey, Dean? I just saw the bodies. This is definitely our kind of case."

At the couple's house, staring at the untidy scrawl of black marker across the cheerful yellow wallpaper of the kids' bedroom, Sam had to admit that it was weird. Even weirder than usual. "What do you think it means?"

"No idea. It's gotta be the kids though." Dean stepped back from the wall.

"Dude, you didn't see the bodies. No kid could do that."

Dean snorted. "Um... demons? Possessed much?"

"Yeah, but seriously? 'Beware of Bill?' What kind of demon leaves a warning?" Sam checked himself. "Besides Ruby, I mean."

"Oh, you just had to bring Ruby into this, didn't you?" Dean muttered. He peered a little closer at the wall and groaned. "Tell me that's not an Illuminati symbol in a top hat."

"Maybe they were trying to warn their parents." Sam continued. "Like a warning against a demon?"

"A demon named Bill?" Dean crouched down and picked a pen knife off the floor. He sniffed it, then sighed. "Course if I'm gonna be wrong, best if it's in the next breath." He flipped the knife around and handed it to Sam, handle first. "It reeks."

"Sulfur?"

"Looked like an iron blade too." Dean stood up. "Whoever these kids are, they had at least half an idea of what they were up against."

"You think they got away?" Sam brought the blade up to his nose, then immediately moved it away again.

"Judging from the lack of torched tweens in the paper, I can say that's a safe bet." Dean said. He started walking towards the door. When Sam didn't follow, he glanced over his shoulder. "You coming?"

Sam gazed at the knife thoughtfully. "I dunno, Dean. Maybe we should stick around. Make sure the demon doesn't show again."

Dean turned. Pointing at the wall, he said, "It's out for blood, Sam. And those two kids knew how to fight it. Who's to say they weren't the target?" He folded his arms. "If we're gonna do this, we're gonna do this right."

"Dean, who's to say they were? They could've just been in the wrong place at the wrong time." Sam folded the knife back into itself, ignoring the crackling sound of the dried blood. He shoved it in his pocket. "Maybe one of us should stay here, just to be safe."

"You sure?"

"Yeah." Sam met his eyes. "There's a reason there's two of us, you know."

"Yeah, I know." Dean rolled his eyes, then headed for the door again. He stopped by the edge of the frame, and turned, fixing Sam with a pointed glare. "But if it turns out the demon is here..."

Sam snorted. "Dude, I know the basics. I'll let you know."

"Okay." Dean turned towards the door again, then looked back over his shoulder reluctantly.

Sam cut him off before he could say anything. "I'm not a kid, Dean. I know what I'm doing. "

Dean nodded grudgingly and walked out the door to the twins' bedroom, ducking under the police tape as he went. A few seconds later, the distant sound of the Impala's engine filled the room. Sam turned back to the crudely drawn triangle on the wall and its hastily written warning. He nodded to himself thoughtfully and muttered. "Guess it's time to call in the big guns."

Four hundred miles away, Mabel took another bite of her banana. "You didn't really plan this far ahead, did you?"

Dipper traced the map with a finger, never taking his eyes off it. "We've gotten this far, haven't we?"

"Yeah. If by 'this far' you actually mean 'stowed away on a banana truck.'"

"At least you got a banana." Dipper hid his face behind the map, his fingers clenching the paper to the point of ripping it slightly along the edges.

Mabel winced and crawled over to him, punching him lightly on the shoulder. "I'm kidding." She plopped down next to him, smiling warmly as she took another bite before tossing the peel aside. "But next time? Let's take the bus."

The truck slowed to a stop. Dipper tensed and looked up from his map. "I thought this truck was heading all the way to Rosenberg. We should have another two hours at least."

A door at the front of the truck opened. There were a couple heavy footsteps on the asphalt outside, then the door shut again with a slam. Mabel met Dipper's eyes. "Hide." He mouthed, crouching behind a large crate. Unsurprisingly, it was labeled 'Bananas.'

Mabel ran towards him, and no sooner had she rolled behind the crate, the back of the truck opened. They both squinted at the sudden brightness. Mabel could see the truck driver silhouetted against the setting sun. He was a large man and his baseball cap was on backwards. He also appeared to have a meticulously waxed handlebar mustache, but Mabel honestly couldn't be sure with the sun in her eyes.

"I know you're in here." He said, his voice gruff. "I've been hearing you giggling since Ashland. Free ride's over. Get out."

Dipper put his hand over Mabel's mouth. Mabel resisted the urge to lick it.

The driver made a funny noise in the back of his throat. "Look. I've been more than generous. I let you come this far. There's a bus station about a mile away."

Dipper met her eyes and put a finger to his lips. She nodded.

The man started to sound irritated. "Look, either get out now, or I'll make you pay for the bananas you ate. And don't tell me you didn't 'cause there's about five more peels on the floor than when I left."

Mabel chanced a peek over the top of the box and bit back a groan. She'd left the peels all over the floor of the truck, in plain sight of the door. Beside her, Dipper closed his eyes and let out an exasperated huff of air. Then he stood up.

"Okay, you got us. Um... we'll get out of your hair now." He grabbed Mabel by the hand and pulled her up.

The truck driver stared at them. "Cripes. You - You're just a couple kids. Are you two runaways?"

Dipper blinked. "Uh..."

Mabel jumped in. "No! Of course not! We're part of a traveling family circus but we got separated from the Ringmaster, and the Bearded Lady told us to change the lion's litter box but we forgot, and Spider-man says 'With great power comes great responsibility,' so-"

The man rubbed his face with his palms. "Okay, okay! Sorry I asked!" He jabbed a thumb over his shoulder, one hand still covering his eyes, "Bus station's that way." He removed his hand and glared at them. "Now, get the hell off my truck."

"Okay!" Mabel said cheerfully, and she hopped out, dragging Dipper behind her. Then they both ran off down the road.

Behind them, the truck driver blinked, then shook his head and walked back to the front of the truck. He revved the engine, then the banana truck sped back down the highway in the opposite direction, leaving a thick cloud of white exhaust fumes in its wake.

Mabel spun on her heel and waved. "Bye, Mr. Truck Driver! I'll be sure to send your regards to the Bearded Lady!" She turned to Dipper with a smug grin on her face. "And that, my dear Dipper, is how you get rid of someone."

Dipper didn't move, then his face broke into a grin and he tackled her in a hug. "Mabel, that was amazing!"

Mabel flashed him a full braces smile. "Well of course it was. Everything I do is amazing."

Dipper rolled his eyes. "And... the moment's gone." He looked down at his shirt. "Ew! You got banana on me!" He tried wiping it off on her sweater, but Mabel jerked away at the last second.

She snorted. "Jerk." She looked in the direction the truck driver had pointed in, shielding her eyes. All she could see was the highway. "So... bus station?"

Dipper furrowed his brow and pulled out his map. "I don't know, Mabel."

"But it's my turn to pick the transportation! Air conditioning, Dipper!"

Dipper stuck his nose deeper into the map. "Well, I dunno about you, but I don't wanna die on this trip. Metal box with only one way out? Maybe not the best idea."

She squinted at him. "Um... Banana truck?"

He finally looked up, folding the map into a tiny square and stuffing it into the pocket of his jeans. He looked her in the eye. "Don't you think a bus going to Gravity Falls would be the first place Bill would check?"

Mabel sighed, sitting down on the narrow strip of dirt at the edge of the highway. "I guess you're right." Then her face brightened. "Oh, wait! Yay! Hitchhiking!"

Dipper set the backpack down on the ground. "I'll take first... what do you call it anyway? Car-hopping? Thumb-sticking-out-ing?"

"They should really invent a word for that." Mabel stuck her legs out straight in front of her and clacked her toes together, swirls of dust swirling outward from her mud-caked tennis shoes.

He hesitated for a second, then stuffed his hands in his pockets. "Yeah. Anyway, I'll go do... whatever that's called." Dipper walked out a few feet in front of her and stuck his thumb out, one hand still jammed into the pocket of his vest.

Mabel stared at her toes for a second, squinting to keep the dust out of her eyes. Then she looked up. "Hey, Dipper?"

"Yeah?" A car whooshed past them, completely ignoring Dipper's thumb. "Oh, come on!"

"Do you think Mom and Dad are okay?"

Dipper didn't say anything for a moment. Another car blazed past them, but he took no notice. Finally, "Yeah, I mean... Bill's after us, right? I'm sure they're fine, Mabel. They're probably sitting in our room trying to figure out what the heck your weird wall message means."

Mabel clacked her toes together again, watching the dust clouds swirl lazily around her feet. "Yeah. You're probably right."

"Of course I am."

Dipper looked back out at the road and stuck his thumb out a little further as a cloud of dust appeared at the top of the next hill. As it approached them, it slowed slightly and managed to come to a screeching halt next to them, startling up yet another cloud of dust. Coughing, they both watched as the settling dust revealed a muddy blue pickup truck with a bug-smeared windshield. The driver's side window slowly rolled down to the three quarter point, where it squeaked and suddenly gave out, and a balding guy in his late fifties peered out at them. "You kids lost?" The cigarette butt in his teeth glowed red-orange and a puff of smoke escaped his mouth, making Dipper cough again.

Dipper cleared his throat and spoke up. "No, sir. We know exactly where we are. We were actually kinda hoping for a ride."

The man smiled a smile that didn't quite reach his eyes, his thin lips revealing a gold tooth that shined coldly in the light of the setting sun. "Where to?"

Mabel stood up and grabbed the fraying backpack. "Gravity Falls, Oregon. Can you get us there?"

"Yes I can, little missy. In fact, I was just heading up there myself."

As Mabel climbed into the backseat of the truck, she tried to ignore the growing feeling of dread in her stomach. She was being ridiculous. Their parents were fine. And as soon as she and Dipper got to Gravity Falls, everything could go back to normal. But try as she might, she couldn't dismiss the feeling that soon, something was going to go incredibly, irreversibly wrong.

A/N: Aaaannd that's a wrap for this chapter. Much thanks goes to my lovely beta Human Customs Still Elude Me, as without her, this fic wouldn't have turned out half as good. Reviews are loved, constructive criticism is always welcome, but unwarranted or unhelpful flames will be given to my Labrador as a chew toy.