Thanks so much to everyone who submitted a prompt, read/favourited/followed and reviewed. I had a lot of fun writing these and I would love to open up prompts again in the future, maybe next time with a theme of some kind.

This final prompt comes from catmoviegrin: Sam is slowly wasting away, and at first they don't even notice, but once they do they can't figure out why (at least for a long time), and things eventually get dire? Meanwhile they're both trying their best to take care of each other. Ending and setting completely up to you.

I warn you that there are some rather disgusting things happening in this one, so if you're particularly squeamish, I suggest you give this one a miss. I definitely got carried away with the monster. Also, while this is chock-full of Sam pain, there's also a healthy dose of Dean.

This one is set during season 10, post Paper Moon.

Moments like these are rare. The air is sticky and thick. The sun is bright and insistent, glinting off the hood of the Impala, wrapping the metal in enough heat to cook an egg. Of course, with hundreds of miles between nowhere and anywhere, the car decides to give up.

The beers in the back seat are, miraculously, still chilled, and Dean pops a cap and takes a swig before fishing the tools out of the trunk. Sam doesn't get out of the car, despite it being a few degrees hotter in there than it is outside, and declines when Dean offers him a beer.

Things are still strange between them both, almost as stifling as the summer heat. Dean wishes he could say something, but what do you say after you tried to bash your little brother's head in with a hammer?

Sam doesn't want to talk either.

It's not just the silence. It's everything else. The two of them used to mesh together like cogs in a well-oiled machine, now there are few glances between them, and even fewer words. Cas hasn't been shy about bringing up the obvious void between them both, but each time he tries Sam is the first to shut it down.

"There's nothing to discuss," Sam always says. "There are bigger things to worry about."

Dean finds his index finger scratching at the flesh of his right arm. The Mark – scar, brand, curse, whatever you want to call it – never seems to stop burning. It doesn't hurt, not really. It's more like an itch that needs relieving. He wipes the back of his hand across his brow and shrugs out of his flannel. Sweat has already soaked through to his t-shirt.

He looks up from where he's crouched and sifting through the toolbox to find Sam watching him through the windscreen. Or, rather, watching the Mark.

"You sure you don't want a beer?" Dean asks, so that Sam's eyes will move up to his face instead. "They're still cold."

Sam shakes his head, but to Dean's relief he gets out of the car.

"You, uh, need a hand?" he asks, gesturing to the tool box.

Dean leans over and pops the lids off the engine. "Let's see what the problem is first," he says. He leans forward and looks around. "What's wrong, huh, baby?"

He catches Sam smiling out of the corner of his eye. It may be the first time he's seen a real smile from him in a long time. Dean wonders, when was the last time Sam seemed happy? When was the last time either of us were happy?

Moments like these are rare; moments where it's just the two of them, a few beers, and nothing around for miles. Just the soft rustle of the breeze dancing through fields, the tinker of the Impala's engine. Normally, they'd talk, or not, but the silence wouldn't be strained like it is now.

By the time he looks up, Sam is staring out over the endless stretches of fields all around, his face is focused, mouth turned down slightly and pinched. Not long after that, after the silence between them has settled back into place, Dean has perked up his baby and they're hurtling across country again.

And not long after that, Sam is devouring his second helping of hash browns and bacon in a grubby little diner just off the interstate. He isn't wearing his sling, it sits abandoned in the backseat of the Impala, but he holds his arm delicately enough that Dean can tell it still hurts. Sam lost a lot of bulk while Dean was gone. Hollow cheeks and sloping shoulders on such a towering man give the impression of a bare tree enduring a harsh winter.

Their feet have been firmly planted in the bunker for two weeks, no signs of anything resembling a hunt in the papers. No inkling of a possible cure for Dean, not that Sam is deterred.

Cas always seems to flutter back in their direction and he's been hanging around the bunker for just under a week, hovering and silent and creepy like he usually is. He stares at Dean almost as much as Sam does, but that isn't really anything new. What is new is the way he's furrowing his brow at Sam with the same concern he's been holding for Dean since the Mark was seared into his arm.

They're eating breakfast – well, Sam and Dean are – and Cas has been staring at Sam since he entered the room. Sam is shovelling down a plate-full of eggs, he'd emptied the entire carton of twelve into the pan and whisked, pouring them onto his plate while they were still runny. When he's done with those, he eats four slices of toast and downs two cups of coffee, all in record time.

Dean finally understands what Cas is staring at. Sam is eating like a maniac. The kid never ate this much even when he shot up two feet over the summer when he was sixteen and his stomach capacity seemed to grow three sizes. The thing about Sam is that, despite being such a behemoth of a man, he's never been a fan of food. Salads? Sure. Smoothie cleanses? Why the heck not. Real food that actually tastes of something? 'No thanks, man, I'm not hungry.'

"Might want to slow down there, buddy," Dean says. Sam pauses mid-chew, already halfway out of his seat and heading back towards the fridge.

He swallows what's in his mouth and says, "huh?"

"I only just bought groceries yesterday, Sam," Dean points out. "You don't need to eat them all within a day."

Sam frowns like he has no idea what Dean is talking about. He says as much.

Cas, meanwhile, is still staring at Sam, eyes narrowed. Dean ignores him and turns back to Sam.

"Just slow down there, Shaggy, okay?"

Sam's brow furrows even further. "Um… okay?" he says, like Dean is the insane one. "I'm going out."

He slips out of the kitchen and Dean listens to his footsteps echoing down the halls before turning to Cas.

"You noticed that, even before I did," he says. "What is this, stress eating?"

Cas turns his squinty eyes onto Dean. "You didn't notice?"

"The eating? Yeah, now I do."

"And how long has he been eating like this?"

Dean thinks back to the diner off the interstate a couple of weeks ago. He thinks back further to almost a month ago when Sam polished three plates of plain pasta off in the middle of the night. Sam's been underweight for a while now, probably since Dean came back with black eyes and skipped off into the sunset with Crowley. Up until now, he'd thought that maybe Sam was just making up for lost pounds.

But Sam doesn't look any bigger. In fact, he looks skinnier.

"He's losing weight," Dean says. Cas nods.

"This is dumb," Sam huffs.

"No, it's not," Dean counters. They've been parked outside the clinic for fifteen minutes and Sam is showing no signs of budging.

"I'm fine, Dean. Coming here is just a waste of time."

"It's really not. Sam, have you looked in the mirror lately?"

"Not really…"

"Well, you're beginning to look like Death, and I mean the horseman. You know, the skinny guy?"

"Yeah. I know him."

"Well, that's how you look."

"Do not."

Dean sighs deeply. "Would you just go in there? Please?"

After a moment, Sam relents, the creaking doors of the Impala groaning shut behind him. In the clinic, the nurse behind the desk stares at Sam for a moment before she can collect herself. Even now, Sam doesn't seem to notice.

"Um, if you could just fill these out and wait over there," she says, sliding a pen and stapled-together papers across the desk. Dean takes them and ushers Sam into a chair. He fills out the form as easily as he would his own, knowing Sam like the back of his hand.

Do you suffer from any allergies? No.

Do you drink? On occasion.

Do you smoke? No.

Is there any history of serious illness in the family? Unless they mean chronic self-sacrificing…

Do you have a history with mental illness?

Dean pauses, then finally ticks yes.

They aren't unused to waiting hours on end in hard plastic chairs, but it's a surprise when they get called through to see a doctor after only two hours. Their doctor looks fresh out of college, she's small and mousey and looks way out of her depth when she glances up to see two giants of men walking into her office.

She glances down at the computer, then back up to them both. "Sam Winston?"

Sam sits down opposite her. "That's me," he says. He sticks his thumb at Dean. "That's my brother Dean. He can wait outside."

"Nope, I'm good," says Dean, taking the seat beside him. The glare he receives is a lot like the sort of look their dad used to get when Sam was a teenager.

The doctor, doctor Lance reads her name tag, smiles at them both. "What can I do for you?"

Dean cuts in before Sam can. "Sammy's been eating a lot lately," he explains, "and I mean a lot. Like, entire cartons of eggs for breakfast."

"Right…" Doctor Lance nods along although it's clear she's a little lost.

"Well, Sam's been eating like this for at least a month and he isn't gaining any weight. He's losing it."

"Oh," Lance says. "Well, that is a little strange." She turns to Sam. "Have you been experiencing any vomiting or diarrhoea?"

Sam visible flushes. "No. No, nothing like that. I feel fine, honestly."

She studies him under her gaze for a moment. "I'd like to weigh and measure you, if that's okay?"

Dean notices that almost everything she says ends like a question, even when it's not. Sam glares at Dean and gets to his feet, following Dr Lance to the corner of the room where there's a set of scales. She measures Sam at a little over six feet and four inches, when he gets on the scales her mouth pinches at the corners.

She and Sam retake their seats.

"Okay. So, you're weighing in at 135.5 pounds, which is underweight for someone of your height. When did the weight loss start?"

"He wasn't this skinny a few months ago. He must have been at least fifty pounds heavier. I don't know why he's losing weight."

"Because I had arm surgery," Sam cut in.

Dean blinks. "You had surgery?"

Sam sighs and looks anywhere but in Dean's direction. "It's not a big deal. It was just a minor surgery."

"Um. Okay," Lance says. "Well, you do have a low BMI. I would normally suggest gaining a little weight, but if you're correct that you're losing weight despite eating a large amount, I suspect something more is at play than just a little weight loss. Sam, would you mind if I take a look at you?"

"Take a look at me?"

"Just a little check-up. I'll check your breathing and your blood pressure."

Sam agrees, but Dean ends up waiting out in the hall. When they're finished, Dean lets himself back in and Lance looks a little more serious than she did before.

"Sam's breathing seems fine, but his blood pressure is low. I think that there's definitely something here that needs to be explored. Unexplained weight loss, especially to this extent, can't be ignored. I would like to refer you to have more tests done. Something like this could be because of a number of reasons and it's best if we figure out what's going on sooner rather than later."

Sam gapes at her. "But I'm fine. Seriously. I feel totally fine."

Lance's eyes are sympathetic. "Maybe you do, but I think you should speak to a specialist and undergo a few tests to figure this out. I assure you, there is an issue here. Hopefully, it's a small issue, but it's something that needs investigating."

.

"Turn in here," Sam says, pointing at a McDonald's drive thru. They left the clinic fifteen minutes ago and are on their way home when Sam's stomach begins to growl. Dean ignores him and carries on driving until the fast food joint is a speck in the rear-view mirror.

Sam glares at him. "What did you do that for?"

"You don't even like McDonald's, Sam. Ever since a happy meal made you throw up all night when you were seven years old," Dean points out.

"But I'm starving," Sam groans, slumping against the window with a huff.

"Quit being a baby," Dean says. "You ate, like, an entire chicken coop this morning. Besides, thanks to you, we have to buy more groceries."

Sam isn't listening, he's sitting upright with his nose lifted in the air, nostrils flared as he sniffs around the dashboard.

Dean frowns. "Dude, what – "

"Ha!" Sam exclaims, popping open the glove compartment and retrieving an abandoned, month-old Snickers bar from its depths. He tears the wrapping off with his teeth, the chocolate is squished and melted, caramel oozing out and onto Sam's fingers. He bites off two thirds in one go. Dean has one eye on the road and another pinned with sick fascination on Sam as he devours the entire candy bar, then licks every last remnants from the plastic wrapping.

"Did you just sniff that out?" Dean asks. He's staring at Sam rather than the road now, and the car veers, so he quickly yanks the wheel and comes to a stop at the side of the road, engine still running.

Sam doesn't seem to have noticed they aren't even moving anymore, let alone heard anything Dean has said. He's too busy lapping melted chocolate off his fingers the way a dog licks meat off a bone.

Weird is normal. Weird is part of their everyday job. What's happening with Sam is weirder than weird. They stopped off at the store on their way back to the bunker and filled up five grocery bags with food, and by the time they make it home Sam has already eaten half the contents of one entire bag.

Even Dean didn't know it was possible to eat so quickly.

He stares at Sam; skinny Sam with crumbs all down his shirt, who doesn't seem to notice anything off. He grabs another bag from the back seat and starts munching on an apple as he heads inside. Meanwhile, Dean scratches at the inside of his arm and tries to think. He might have thought all of this was just some freaky medical problem, but after watching Sam sniff out a candy bar from underneath all the crap in the glove compartment he's now sure it's more familiar than that.

He balances the last three grocery bags in his arms and heads inside. Cas is in the kitchen, watching Sam with squinted eyes and a tilted head, the look he reserves for something new and fascinating. Sam, of course, is eating another apple and assembling a ridiculously thick sandwich at the same time.

Dean catches Cas' attention and waves for him to follow him to the library. If Sam even noticed either of them being in the room, he doesn't show it.

"Strange," Cas says, once they're alone in the library.

"You think?" Dean snaps. "Do you know what's up with him or not?"

"I don't," Cas murmurs, eyes flicking in the direction of the kitchen. "The grace I have now – it isn't my own. Normally, I would be able to find the cause of the problem…"

"But your mojo's not up to scratch," Dean finishes for him. He sighs and finds his fingers once again under the crook of his elbow, tracing the raised flesh of the Mark. It burns, cries for attention, but Dean has more important things on his mind. 1) find out what's wrong with Sam, 2) fix Sam, 3) look for a cure for the Mark.

They're set up at the library tables with books and files covering every inch of the surfaces. They've been reading for about half an hour, everything the Men of Letters have on supernatural weight loss and excess eating, when Sam comes wandering into the room with a bag of chips in hand. He tosses a chip in his mouth, crunching obnoxiously loudly, frowning at the two of them.

"What are you doing?" he asks, taking a spare seat beside Cas. He glances down at one of the books, at a rather unpleasant black-and-white photo of a victim of a wasting curse. His mouth curls downwards, "What's this?"

Cas glances at Dean, expression blank. Dean sighs and says, "Something's up with you, Sam."

Sam's eyebrows raise an inch. "Something's up with me? Dean, you're the one with the Mark of Cain. Don't you think we should be trying to fix that instead of reading… whatever it is you're reading."

"You don't even see it, do you?" Dean says. "Sam, you're skinny as hell, despite eating non-stop. How are you not full?"

Sam shrugs. "Dunno. I'm just hungry," he says, then tips the bag of chips up over his wide-open mouth to swallow down the last of the crumbs.

"And don't you think that's weird, Sam?" Dean points out. "You're never hungry. No one gets this hungry."

Sam rolls his eyes and glances at Cas. "He's being ridiculous, right?"

Cas glances down at the table awkwardly. "Not really," he says, looking up at Sam again, eyes narrowing. "Something is off. I can't tell what exactly it is, but something isn't right. It's like… a void."

Sam blinks. "A void?"

"Yes," Cas says. He leans in close to Sam, Sam leans away. "Something that begs to be filled."

"O-kay…" Sam says, climbing out of his seat. "Well, you guys can waste time all you want, I'm going to look for a cure for Dean."

Then he's out the room. Dean glances over to Cas and whispers, "A void? Like an 'I'm sad and life is meaningless' void? Or are you saying there's a black hole inside my brother that wants to be filled with Big Macs?"

Cas is staring at the door Sam just exited through. He tilts his head and says, "I don't know. I can just feel a hunger. A darkness."

"What do we do?"

"I don't know. But I suggest he doesn't leave the bunker."

Sam finds a case. Of course, he does. He's a goddamn news perusing freak.

"No."

"What do you mean 'no'?" Sam demands, tapping away at his computer and eating an entire packet of refrigerated frankfurters at the same time.

"I mean no, Sam. We're not up for a case right now. Not with you…" he cuts of, gesturing a hand at Sam's entirety.

"What?" Sam says, glancing down at himself. He's sucking on the end of one of the sausages, which gives Dean plenty of ammo that he won't be using. The amount of dick jokes he could be making right now, but his mind is elsewhere. Namely, focused on Sam's skeletal frame.

Sam still doesn't seem to notice anything wrong, which makes Dean wonder if this is more than just a physical ailment. Anyone with eyes could see how Sam looks; stick thin. He keeps having to hoist his jeans up on his hips, which are bony and likely sharp enough to cut something. Dean's surprised Sam is still getting around on two feet.

"You're sick, Sam," Dean says, like he's been saying for a while now, but it only seems to go in one of Sam's ears and out the other.

"I'm not sick," Sam says, rolling his eyes like it's the dumbest thing he's ever heard. "You've been taking hunts with a cursed mark on your arm for months."

"It's different," Dean bites back.

"Yeah, because there's nothing wrong with me."

Dean takes a deep breath, clenching and unclenching his fists under the desk. "How much do you weigh, Sam?"

Sam shrugs. "I don't know. What did the doc say?"

"That was a week ago. You've lost weight since then."

Sam's lips are pressed into a thin line, an indicator that his patience is wearing thin and the conversation is most likely over. "Fine. You don't want to take this hunt?" he says. "I'll go by myself."

Dean's more than ready to bite back, but the moment Sam gets to his feet he stumbles, grabbing the edge of the desk for balance. Dean is up, out of his chair and over by Sam's side by the time Sam's only managed to peel his eyes back open.

"You okay?" Dean asks, dropping a hand onto Sam's shoulder. He nearly recoils when he feels just how bony it is.

"Just got dizzy for a second," Sam says, but he's breathing through his mouth, colour leeching from his face.

"Yeah, you got dizzy because you're sick," Dean says. Without a word, he pulls Sam's arm over his shoulders and guides him slowly towards his bedroom. "You're going to rest, little brother. Let me and Cas take care of this."

"Supposed to be fixing you," Sam mumbles, head leaning tiredly against Dean's arm.

Dean sighs. "The Mark's my problem, Sam. It's my mess. Don't think about that until you're better."

Dean dreams of a hammer. Long and slender, a gentle weight in his hand, just the right balance for the perfect swing. The metal end of it is heavy, smashes right into the wall if you put enough muscle behind it. He's stalking the hallways, red light pulsing, the mark on his arm sings with the excitement of it all. It's a game of cat and mouse.

Sam has his back to him, head ducked around the corner, watching for Dean, not knowing he's right behind him. Dean moves softly, arm pulling back and swinging hard just as Sam spins around, eyes wide and terrified and –

Dean wakes up suddenly, sweaty limbs tangled up blankets. He flicks on the bedside light and glances at his arm where the mark is looking more irritated, the skin throbs. He pulls his sleeve down and takes a few breaths. His mouth is dry, tongue sticking to the inside of his cheeks. He gets unsteadily to his feet and stumbles, eyes still adjusting to the light, out into the hallway and towards the kitchen.

He pauses when he sees Cas standing in the kitchen doorway, eyes focused inside the room. There's a clang of pots and pans, and Cas turns to Dean, holding a finger to his lips.

"What's going on?" Dean whispers, joining him in the doorway. Sam is in his pyjamas, crouched on the floor by the fridge, packets of raw bacon, chicken and mince-meat on the floor in front of him. He grabs a fillet of chicken breast, pink and shiny and raw, and puts it in his mouth, tearing a tough chunk out of it and chewing slowly.

Dean makes to start forward, but Cas stops him with a hand to his chest.

"Sam is sleeping," he says.

Dean looks over again, and sure enough Sam's eyes are glazed and out of focus. He has to look away again when Sam scoops up a handful of mince-meat. His stomach churns at the sound of Sam's chewing and he clamps his teeth together in the hopes that he won't throw up.

"We have to stop him," he says to Cas. "He's going to make himself sick."

"I tried stopping him," Cas replies, eyes not straying from Sam. "He wouldn't move. He even – he was vicious. Like an animal."

Dean glares at him. "So, we just let him get on with it? He's gonna get salmonella or something."

"I don't think that's an issue," Cas says. "I don't think it's Sam who's eating this. There's something else here. I can feel a presence in this room."

"Demon?"

"Not a demon."

"What is it, then?"

"I don't know, Dean," Cas says, sounding frustrated. He opens his mouth, ready to say something more, but Sam is getting to his feet. He stumbles towards them, hands and chin stained with grease and something watery pink. Dean and Cas part to make room for Sam to pass by them into the hallway.

"Sammy?" Dean says tentatively. Sam keeps walking, so Dean grabs his shoulder and it's only then that he turns around. He shoves Dean against the wall, teeth bared, eyes turned a milky white. Dean bares his teeth right back, the Mark on his arm twinges. He pushes hard, sending Sam into the opposite wall, then he pulls back his fist and sends it flying right into Sam's face.

One hit sends him sprawling to the ground, unconscious, a line of blood running from his nose. Dean shakes out his fist and turns to Cas.

"Help me get him to the dungeon."

Sam, naturally, is confused when he wakes up chained the centre of a devil's trap. He stirs, face scrunching as he begins to feel the effects of Dean's fist to his face, then peels his eyes open to look up at Cas and Dean.

"What's going on?" he asks, and makes to sit up. Only then does his notice the cuffs and chains around his wrists. He jerks them experimentally, frowning when they don't budge. "Hey!" he snaps, now moved on from confused to pissed.

"It's for your own safety, Sam," Cas says.

"Safety," Sam repeats, glancing around the room. "What the hell? Did you kidnap me from my own bed? What's going on?"

"Something's wrong with you, Sam," Dean explains.

Sam glares at him. "Right back you."

"Dean's right," Cas says. "There's something else in this room, Sam. It's dark."

"The Mark of Cain," Sam points out. "You sure you're not just mixing things up?"

Cas glances warily at Dean, or rather, at the spot on his arm where the Mark is etched. "The Mark of Cain, yes, that's a darkness. I feel that all the time, but there's something else. It's getting stronger by the day, and it's attached to you, Sam."

Sam snorts. "This is ridiculous. Would you unlock these and we'll go upstairs and pretend this never happened?" he jangles his chains.

"We can't do that, Sammy," Dean says. "We can't even be sure it's you talking to us right now."

"That's ridiculous. Of course it's me," Sam sighs exasperatedly. He looks at them both with a steady gaze and says, "Don't you see how crazy this is?"

He sounds like Sam. He's wearing a very Sam-like expression on his face. But he still has the stains of the raw meat he devoured only a little while earlier clinging to his skin. His shirt hangs off his frame, it practically swamps him. His cheekbones are high and pronounced, his fingers are bony, his collar bones are sharp where they peek out from under his shirt. Sam's never been so thin, not even when his teenaged growth spurt left him more bones than boy.

He looks sick. He looks like he could be dying.

"We'll fix this," Cas says, and Dean isn't entirely sure who he's speaking to.

"Paracitus Inanis."

"What?"

"Paracitus Inanis," Cas repeats. "Also known as The Empty Parasite. It is a long-extinct supernatural species of parasitic worm."

"You think Sam has a parasite?" Dean asks, leaning across the table to get a glimpse at the book Cas is reading. There's a grisly drawing of a long worm with white eyes and a circle of razor sharp teeth. "Huh. Looks kind of like the Kahn Worm."

"Kahn Worm?"

"One of Eve's wacko creations," Dean explains. "It got inside peoples' ears and controlled their brains. You think Sam has worms?"

"Worm," Cas corrects. "It says here that Paracitus Inanis must hatch from the egg and grow through infancy inside a host. Once the worm is too large to be contained, it will exit the host."

So much about all of this is too disgusting to think about, but he has to ask. "Exit the host how?"

Cas clears his throat and recites from the book, "When the parasite abandons its host, it exits the same way it enters, via the gullet."

Dean feels his face twist. He has seen the grossest of the gross, but this is something else. This is like something out of Alien. How did Dean miss Sam getting attacked by a Facehugger?

"Sam was hunting while you were… gone," Cas says, answering Dean's unspoken question. "Perhaps that was when he contracted the parasite."

Dean sighs and rubs his hand over his tired face. He hasn't been sleeping much since he shed the black eyes. Nightmares. And guilt. And now, there's a parasite in his brother that needs removing. "How do we get rid of it?"

Cas glances back down at his book. "The parasite relies on the host to be fed, which is why Sam has been eating so much but losing weight at the same time. If the food supply is cut off, the worm will search for another host."

"So, we have to starve it?" Dean asks.

"We have to starve Sam, too," Cas corrects. "He's already malnourished. This may kill him."

"We can't just leave it in there," Dean says. "We keep an eye on him the whole time, if something goes bad – you got any mojo left?"

Cas looks a little embarrassed, if it's possible. This whole stolen grace thing must weigh on him more than Dean even cared to think about. It's strange sitting in the library with him, researching like he and Sam would for a case. It's almost like Cas has filled Sam's vacant role.

"I'm not letting him die," Dean says. "Not after everything."

Cas can't give him an answer to that.

The ridge of Sam's spine is steep and sharp, protruding under his skin like there isn't enough room. The shape of his ribs is harsh, like hollowed out grooves down his side. His shirt has been shed, the fabric caught against the manacles. He's pale and sweaty, drops of moisture sliding down his skin.

The moment Dean and Cas open the doors, and the light from the store room comes flooding inside, he cants his head to the side and observes them. The desperation he'd had when they'd locked him in is gone, because maybe Sam is gone. There's no please, guys, don't do this or I'm fine. I'm me.

Just quiet.

"We figured out how to fix this," Dean says, and Sam's eyes flash over to him.

"And how will you fix this?" Sam says, and Dean knows it isn't Sam. Sam wouldn't smile like that.

"You hungry?" Dean asks. Sam's smile drops and his eyes narrow. Dean grins. "Well, you slimy bastard, you're going on a diet."

"We'll give you the chance to leave now," Cas offers. "Before things become difficult."

"Difficult for me, or difficult for you?" says Sam. "I'm quite comfortable here, thank you. Besides, if I leave now, you'll smite me with those God-given powers of yours…" he breaks out into a wicked grin. "Oh, wait. You're running on a low battery. Barely even Angel anymore. What can you do to me?"

"I was hoping you'd ask," Dean says, holding out the blowtorch from where he'd had it behind his back. "I always liked my meat a little crispy."

Sam pales. "Do what you like," he says. "I'm not leaving. And you can't hurt me without hurting your brother."

Sam, or rather the parasite inside him, decides on the silent treatment after that, turning around to face away from them. Dean and Cas pull up chairs and wait. And wait. And wait. He's teaching Cas how to play poker – finally Cas' constant blank expression comes in handy – when things begin to change.

Sam is restless, shifting inside the devil's trap, tugging on his chains.

"Feeling peckish?" Dean asks. The thing glares at him.

"You're going to kill your brother like this," it says, gasping. "Not that you'd mind. You tried to bash his head in not long ago, didn't you?"

"Trying to play mind games?" Dean says. "Cute. Shut up and get out, would you?"

"I will get out of these chains and your flesh will be the first thing I feast on."

Dean rolls his eyes. "Threats ain't going to work either."

"Dean, it might be best not to engage," Cas suggests, eyes still on their game of poker. "It will be some time before it leaves Sam's body, and it will leave."

Dean shrugs and returns to the game, ignoring Sam hissing at them over his shoulder.

"Please," Sam gasps. Not-Sam. He's curled up on his side, shivering like he's freezing cold, covered in sweat with his hair clinging to his forehead over milky white eyes. "Please, you're killing me."

"That's the plan," says Dean. His voice betrays him by cracking, so he straightens his back and folds his arms over his chest. He has to remember that this thing on the floor isn't Sam. Jesus. How many times has Sam not been Sam?

"You're killing your brother," it says.

"No, you're killing my brother," Dean bites back. "Get the fuck out."

"Do you even care?" it asks, shuddering. "Your brother is in pain, and all you do is sit there and play cards. You can feel it, can't you? That Mark is leeching away the last of your humanity. You might not have black eyes anymore, but you're not one hundred percent human. It's only a matter of time. I know it, you know it, even Sam knows it. You're going to kill your brother and you're going to like it – "

"Dean!" Cas shouts.

Dean is on his feet, Sam's neck clamped between his fingers. He lets go and jolts back like he's been electrocuted. The thing inside Sam grins.

"There it is," it says.

Dean is breathing hard, chest heaving, hands shaking. The skin of his inner arm burns in a way that's almost a relief. Cas is lingering over his shoulder and Dean can feel where his arm is reached out and lingering in the air, not daring to take hold of his shoulder. On the floor, Sam is wasting away, pale and skeletal, grinning from ear to ear, skin creased around the milky whiteness of his eyes.

Cas finally grabs his shoulder and pulls him back into the store room.

"Take a walk," he says, hard-eyed.

"But – "

"Go."

Dean doesn't wander far. He makes it up the stairs and down the corridor until he comes face to face with the dent he made in the plaster, a dent he'd intended to make in Sam's skull. Sam, who is now chained to the very same spot Dean was weeks ago, wrapped up in something dark and oily and vicious, just like Dean was. But Dean's darkness was himself. Sam was just in the wrong place at the wrong time, without anyone to watch his back.

If Dean had been there, none of this would have happened.

He stares at the hole in the wall, thinks thank god I taught Sam to be quick. But God was never around to thank. He's breathing more steadily now, but his heart is still racing, more from fear than anything. Sam could die. For weeks, Sam has been dying and Dean never even noticed.

He brushes his fingers along the dent, thinks about how he should fix it when he has the time, then he turns back around and heads for the dungeon.

There are god-awful noises coming from beyond the store room. It's wet and thick, hacking, coughing, spine-curlingly sick. Cas is hovering more than standing, like he's torn between going to Sam's side and staying right where he is. Dean pauses at the edge of the devil's trap, not because he's afraid of what's inside, but because he's worried if he steps over he might not be able to get out again.

Sam gags and spits out a gob of spit that's grey and bubbling. He glances at Dean and his eyes are hazel and wet, the whites of them are turning red. He shudders and hunches over, neck straining. His limbs are shaking, only barely keeping him upright.

He hacks again, and this time the head of something thick and sluggish slides out of his mouth. Sam's eyes go wide and he does a backwards crawl as far as the chains will let him in an attempt to escape it. The worm is more like a snake, longer than Dean's arm, slithering up Sam's throat and out of his mouth like something out of a horror movie. But Dean has seen horror movies, and they're nowhere near as bad as real life. Nowhere near as awful as this.

The second the tail is out and slapping the concrete dungeon floor with a wet smack, Sam crumbles. His arms and legs fold and he lies there on his side, heaving breaths, still gagging. The thing makes to slither in Dean's direction and he stumbles back, but it's faster than he'd expected. It begins to curl around his leg and he can see its milky white eyes and razor sharp circle of teeth. Trying to kick it off only makes it cling tighter.

Cas appears, the palm of his hand lit up with pure light bright enough to blind Dean for a second. The pressure around his leg releases, then there's frantic hissing and the smell of burning meat. Dean peels an eye open and sees a charred streak across the floor beneath Cas' feet.

At the centre of the room, Sam rolls onto his back with a deep, rasping breath. Dean crawls over and pats Sam's cheek until he opens his eyes.

"God…" Sam mumbles, then coughs. There's oily, grey saliva running down his chin. "That was…"

"Disgusting," Dean finishes. Sam gives a weak nod of agreement, and closes his eyes again. Dean nudges his shoulder. "No sleeping yet, okay?"

"M-hm," Sam answers, still not opening his eyes.

Cas is there, crouching down by Sam's head. He places his palm over Sam's forehead, emitting a soft glow that makes Sam shudder.

"I've healed some of the internal damage," he says. "But there's a lot I can't heal. It will take time."

Dean sighs and rubs a hand over the bare skin of Sam's trembling arm. "Let's get you to bed, buddy."

Sam's mouth curls with distaste as Dean holds out a spoonful of oatmeal. He turns his head so there's no place for it to go but back in the bowl. Dean sighs and drops the spoon with a clang of metal against ceramic.

"You need to eat, Sam."

"I'm think I'm put off eating for life."

"Eat."

Sam drops his head back onto his pillow. He doesn't look much better than he did when he was hosting a supernatural parasite. He hasn't put on any pounds yet, and it makes him look like a chemo patient. At least he's clean and has some colour back in his cheeks; the only things keeping him from looking like a corpse.

"If I eat anything, I'll throw it back up," Sam says.

"Good thing I brought a bucket."

Sam glowers, but he doesn't have enough energy to really mean it. All he's done the past couple of days is sleep or throw up. Dean's getting more worried by the day. He was stupid to hope that Sam would just bounce back after everything that's happened.

"I'm tired," Sam whispers, eyes already closed. "I'll eat tomorrow."

Dean pats his hand. "Fine. Tomorrow, or I'm taking you to the hospital to get a tube inserted."

Sam doesn't register the threat, having already drifted off to sleep. Dean tugs the bed quilt up over Sam's chest, staying seated by his side a little longer. Scratching absently at the Mark, he lets the guilt settle in his stomach to turn sour. Sam's cheeks are hollow, eyes sunken, wrists slim enough for Dean to circle and have his fingers meet.

There's a thought at the back of his mind that tells him Sam is weak and defenceless. He wouldn't be able to stop an attack. Not from a monster or a person or a hammer.

There's something parasitic in Dean that needs to be killed.

Thanks so much for all of the prompts! And thank you for reading! (I hope this didn't gross you out too much)