Disclaimer: I have no affiliation with Castle or Supernatural. Not for profit.

"Really Castle? That's what you're going with? A ghost?" NYPD Detective Kate Beckett raised her eyebrows at the writer as she crouched beside the body. It was messy, but not the worst she'd seen. The man's throat was torn out, his chest in ribbons. Blood pooled beneath him, soaking into the worn grey carpet.

"What else could it be?" Richard Castle was practically bursting with excitement. He began ticking things off on his fingers. "The door was locked on the inside. There was no weapon. And there's an eyewitness who swears up and down that she saw the man's wife who has been dead for four months come into the apartment twenty minutes before he died. I'm just saying that sounds like a ghost to me."

"First of all, Castle, the eyewitness is ninety-six, and even if she wasn't, memories get warped between seeing something and describing it. Secondly, if it was a ghost, why did it use the door? Why didn't it just walk through the wall?"

"Good point. Oh!" Castle had a flash of inspiration. "It's not a ghost, it's a zombie!"

Beckett rolled her eyes and turned to look at Lainey. "Is there anything else you can tell us?"

The M.E. looked up from examining the body. "Time of death is between nine and ten last night. I can't be sure of cause of death until I get him back to the lab," she gave Castle a pointed look, "but some kind of weapon was definitely used. Nothing I immediately recognise, but these injuries would be impossible without something sharp, possibly multi-pronged. I'll know more when I get a better look."

"Thanks, Lainey." Beckett left her there to finish preparing the body for transport to her autopsy room and went to see what Ryan and Esposito had dug up.

"No dice," Esposito announced as she approached, "Except for the old lady who found the body, no-one saw or heard anything. There's no-one to corroborate her story about the wife, and get this – nobody even knew his name. They didn't know what he did for a living either, just that he was gone a lot at night. One of the neighbours said he'd sometimes disappear for days and come back limping or bruised, but he never asked about it. It's that kind of place: don't ask, don't tell. I get the feeling that the old lady only knew about the wife dying because she's one of those nosy types who barges in and won't leave until her curiosity is satisfied."

"Okay, so we've got a guy who only spoke to one person in his whole building, had recently lost his wife, and often disappeared and came back hurt. Ryan, you got anything?"

Detective Ryan made his way over, a perplexed look on his face. In his gloved hand, he held several I.D.s. "Oh yeah," he said, "You've got to see this. The guy has fourteen fake I.D.s, and not just fake driver's licences. FBI, Health Department, you name it. All quality work and in different names. We can't even be sure what his real name is."

"He's been impersonating a federal agent?" Beckett frowned.

"That's not even the weird bit," Ryan continued, leading them into the bedroom and across to the wall between the apartment and the one next to it. He knocked on it.

"It's hollow?" Castle asked, wandering up to see what the excitement was about.

"Hollow, but not empty." Ryan knelt and ran his hand along the bottom of the wall until he found a tiny indentation. He pressed down on it. There was a quiet click and the panel popped out. Ryan slid it to the side.

The wall was full of weapons. There were shotguns and handguns and knives of all shapes and sizes, arranged neatly on the back wall for easy access. There was a double-headed axe, and a scythe sharpened to a razor edge. On a solid shelf sat six hand grenades, military issue, the pins thankfully still in place. Underneath were draws of ammunition. Beside them leaned what looked suspiciously like a flame-thrower. Finally, on the floor beneath the weaponry sat three sacks of rock salt.

"Ooh, ooh, I know this one!" Castle's eyes had widened at the array, "He's vigilante who killed his wife and she came back from the dead to get revenge!"

"There's no such thing as zombies, Castle," Beckett said. She gazed at the weapons. "Although I'm starting to think you might be right about him being a vigilante. But we can't jump to any conclusion. First priority is I. the victim, then we can figure out why he's got a wall full of weapons." She left Ryan and Esposito to pack the weapons off to ballistics while she and Castle followed up the fake I.D.s.

XXX

Half an hour later, she and Castle were back at the Precinct, standing in front of the murder board.

"Seriously, though, it's weird... this is the emptiest I've ever seen the whiteboard," Castle commented.

Beckett finished tacking up the victim's photo. So far there was only a single name in the witness column, accompanied by 'wife?' under suspects.

"We'll just have to dig harder. Find out more about the wife. We've only got the neighbour Mavis Finkle's word for it that she's dead. Maybe she just left him, or faked her death. Or maybe she really is dead and it wasn't her that Mavis saw at all."

She could practically see Castle's brain churning out impossible theories about CIA agents and evil twins, but he restrained himself and just asked: "Do we know what the wife looks like?"

"Mrs Finkle is with the sketch artist now." She started a new column on the board, block letters in black marker. Fake I.D.s. She listed them: FBI; Health Department; NYPD; Homeland security; an I.D. listing him as a security guard; three driver's licences, all from different states and under different names; two different press passes; animal control; park ranger; CDS; and an LAPD badge. "What could he possibly need all of these for?"

"Honestly? I got nothing." Castle frowned at the board. "Can we work out who made the I.D.s?"

"Maybe some of them. This is high quality work. You need specialised equipment to make these. He's obviously not making them himself. Maybe if we track down other I.D.s we've confiscated and compare them we can narrow it down, but there's no way to know for sure."

It took them nearly two hours to sort through the confiscated I.D.s until they found a possible match. It was a fake licence that bore the same features identifying it as a fake as one of the victim's licences. The work was very high quality, and it was almost impossible to tell it wasn't genuine. The teenager who'd been caught with it had dobbed in the maker, so they had a name: Jeremy Locke. Locke's workplace was listed as a graphic design studio not far from the precinct.

XXX

As Beckett and Castle were leaving to pay the artist a visit, Esposito stopped them. "Yo, Beckett. We got something."

Beckett made a detour over to his desk.

Esposito continued: "The ballistic report isn't back yet, but far as I could tell the weapons were all real – and well used – especially the sawn off shotguns. But – and this is really weird – " He picked up a shotgun shell from his desk and pried the end off before tipping out its contents. A small white pile formed on his desk.

"What is that?" Castle asked.

"Rock salt. There were hundreds of them, all the same."

"What would he be shooting with rock salt?" Beckett wondered.

"Hell if I know," Ryan said, "But there were also bullets that are almost definitely made of silver. And this." He handed her a piece of paper, crinkled and somewhat bloodstained. There was a sketch of a man's head on it, well shaded and probably done by a professional. Almost like a police sketch artist had done it. "It was lying under the body. Lainey found it when she was moving him. We think whoever murdered this guy might have been looking for the man in the sketch."

Beckett examined the picture closely, with Castle peering over her shoulder. He was standing unnecessarily close, but she didn't protest. Sometimes it was easier just to let him be. And secretly she kind of liked it. Not that she'd ever tell him that. The sketch was in pencil, a little smudged from blood and having a body lying on it, but she could still make the man out clearly. He was extremely handsome, even in black and white. Big eyes, straight nose, high cheekbones, a perfect mouth. He had short, light coloured hair, and a smattering of freckles. He looked vaguely familiar. She handed the picture back.

"You guys run him down, we're going to talk to a guy who might have made the I.D.s," She said.

"Wait," Castle reached for the picture, a slight frown of concentration on his face. "I know who this is! It took me a second because I haven't seen a picture of him in a while, but that's Dean Winchester. I researched him for Devil's Storm. It was about a series of ritual satanic killings. Storm has to infiltrate a satanic cult an almost ends up being brainwashed into believing the teachings..."

"Castle," Esposito interrupted, "Dean Winchester?"

"Oh, right. Anyway, his father apparently had a psychotic break after his wife died in a fire. He started believing in monsters and brainwashed his sons Dean and Dean's younger brother Sam into believing in them too, and spent over twenty years travelling the country, killing 'monsters'." Castle put the word in finger quotes. "Nothing could ever be proved against the father, but after he disappeared, the brothers took up the family business. Dean was wanted for several murders, and both brothers for a whole list of things from bank robbery to grave desecration to credit card fraud. They were known for incredible escapes from custody and for winning over people in the lives of their victims. Dean faked his own death once, and both brothers are thought to have died in an explosion a few years back."

"Now that you mention it, I think I remember his picture doing the rounds a few years back. You guys find out if it's really him, and if it is I want to know why our murder victim was lying on his picture."

"Dean and Sam, mother died in a fire, hunting monsters... Why does that sound familiar?" Ryan mused as he took the sketch back from the writer and turned to his computer.

XXX

Beckett took Castle with her to the graphic design studio where Jeremy Locke worked. It was a small place that worked mostly in computer graphic design. The room was filled with a variety of specialty printing equipment, all of it whirring and humming busily as they walked in. The man they were looking for was bent over a printer, adjusting the settings when they approached him. He glanced up and smiled smarmily.

"Can I help you?"

"You tell me, Jeremy," Beckett showed him her badge. "NYPD, Detective Kate Beckett. We'd like to ask you some questions concerning your side business."

"I don't have a side business," Locke protested. He was in his early thirties, wearing an outfit ten years too young for him, and had greasy hair and shifty eyes. He wiped ink-stained palms on his jeans.

"Cut the crap, Jeremy, we know about the I.D.s. In fact, one of them just turned up at a murder scene."

"M-murder?" Jeremy stammered.

"You'd better start talking, or it's not looking good for you."

Jeremy Locke nodded, swallowing. "What do you want to know?"

Beckett showed him the false I.D. – an Alabama driver's licence in the name James Wilson – and watched his face as he examined it. "Tell me about this. When did you make it? Is there anything you can tell me about the man you made it for?"

"It was a few months ago. Dude wanted multiple I.D.s. He didn't say what for, and I didn't ask. He was a scary guy, y'know. I didn't want to make him mad, so I got him his licence and a security guard badge and a..." Locke trailed off, mumbling.

"A what, Jeremy?" Beckett demanded.

"An-FBI-badge," Jeremy ran the words together in a rush, "He had a gun, man. I mean ma'am... detective. I mean, he didn't point it at me or anything, but I could see it in his pocket, and he was bigger than me, and his face was hard... and it was the way he carried himself."

"How?"

"Like a soldier."

"Did he give you a name?" Castle made his contribution.

"No," Locke replied, "But he told me to hurry up because there were demons on his ass."

XXX

Beckett let Locke go with a warning to shut down the illegal portion of his business instead of charging him, as a reward for co-operating. They weren't much further ahead, but could at least eliminate a few possible identities, and had a better picture of what the man had been like. Lainey called as they were heading back to the precinct, and they changed course to visit her.

When they arrived, Lainey was waiting for them, corpse laid out on her examination table. She'd cleaned off most of the blood, so the wounds were clearly visible, looking like nothing Beckett had seen before.

"What have you found?"

"Oh, we'll get to him in a minute. He's not going anywhere. I was just paid a visit by a couple of guys who were definitely not feds."

"Intriguing," Castle interrupted, "Locked doors, people rising from the dead, satanic serial killers, and people posing as FBI! Best case ever!"

"Anyway," Lainey continued, holding up a finger for quiet, "Did you see the sketch I sent over? Because I'm pretty sure that the guy in the picture was one of the men who came and asked questions."

XXX