This is AU as of 5.21. It's also kinda Kripke'd by 5.22. No heavy spoilers for Season 5 since it's AU, but 5.14 is pretty important for the premise.

Gen. Violence. Dark themes. Schmoop.

Set between 5.18 and 5.20.

There was a table slapped together from boards and sawhorses, cluttered with salt and jugs and funnels and strange, mispurposed tools like the wire grill brush matted with human skin and fat. Iron chains. A turkey baster. Elbow-length gloves and wading boots. Duck tape and marker pens. A 100cc syringe and the biggest hypodermic needle in the clinic.

The abandoned shipping container was cold and echoing, but it was private, oh, hell, was it private, rusting in the middle of the woods like it was waiting for the Boxcar Children. It got Winchesters instead. Sam gripped Dean's tense shoulder as he stared down stonily at the one bowl of holy water that didn't have demon blood in it, and carefully sponged the spatters off Dean's face, away from his mouth.

"You're good," he muttered when he was done.

Dean grabbed the rag and smoothly, efficiently, wiped off his arms, neck, and hands.

"Dean, you didn't have to—" Sam winced. "I mean, I could've—since I'm going to anyway—"

"Well, now we know," Dean said.

They turned to look at the demon, at what was left of it, stripped down to boxers and splotched all over with chemical burns from holy water and salt. It was still dangling by its wrists from ropes in the ceiling and walls, feet hobbled to cargo rings in the floor, an IV of bagged blood running into a vein in one arm and an empty tube running out the other arm into a gallon jug.

They'd brought the O-neg in case the host was alive. Now Sam was going to have to get more.

"Fifty demons," Sam repeated to himself. "How long do you think they've had him?"

"Long enough to get their kicks in before they bait the trap." Dean shucked his t-shirt and flung it savagely at the equipment table before grabbing the rest of his clothes. "Any better ideas yet?"

"Nothing fast enough." Sam licked his lips and scratched the back of his neck. "If I shove you through a table and strangle you again, go ahead and hit me in the nuts."

"Aw, Sammy, you do care."

Sam swallowed bile. "I mean it. Don't let me hurt you, don't let me hurt Cas—you're the only one who can keep me on target, and even then—"

"Sam," said Dean, calm, present, with it, as if the robotic prowling thing with the shark smile who'd protested, fearful and mutinous, "I'm working on a concept—you said I could handle it" when Sam had come in and tugged him away from his work just ten minutes ago, had never existed. "Come on, Sam, that was like—like sparring on PCP, or something. Stop angsting and think up another plan A."

"Dean—"

"Drive. Think." Dean slapped him on the shoulder and shoved him at the door.

"Are you—"

"Fine. I'll handle it."

They stepped out into the humid night with the moon overhead and the crickets singing, and the lantern splashing a golden strip of light across the car. Sam put on the headlights and rumbled down the rutted track; in the rearview mirror, Dean slumped on a log. Thinking up alternate plans. Sam hoped the clinic they'd raided wasn't crawling with uniforms by the time he got back, otherwise…

Fifty demons to burn out. Sam wasn't sure it was physically possible to drink enough blood.

Sam had returned with twelve quarts, anticoagulant, and an armload of sport bottles with straws. Not a better plan A.

They'd flushed all the blood through the host before killing him and the demon, and burning rubber for the station. The police station in Argonne. The station that didn't have a single un-possessed human being, where the hellhounds howled day and night, where Castiel was suffering the most refined tortures it was possible to inflict aboveground. The incredibly obvious trap.

"Two minutes."

They were in a stolen car now, white Honda Civic, the interior vandalized with sigils for restraint, secrecy, and protection on every smooth surface. The station popped into view as they rounded a corner, and Sam reached into the back for a gallon jug.

Dean closed his eyes as he pressed the accelerator. "Go." Cas had no idea what he dragged up from Hell.

Sam started chugging. Plastic crinkled, breaths came slow and intermittent. The station was getting bigger, every other car was a blue-and-white. Sam dropped the jug and reached back for number two, coughing.

"Hang on," Dean barked, hauling on the wheel, and spun the back bumper into station's main drive with a shrieking donut. He set the parking brake. "Ready?"

Sam polished off the second jug, and there was a vacant look in his eyes, in the way he reached into the back seat for a sports bottle without even noticing the blood on his chin, in the way his eyes drifted over Dean like he was just part of the upholstery.

A cop—demon—was sauntering over to investigate. They had to kill it before it saw their faces.

"Sam. Clock's ticking."

Sam shut his eyes and paused in Hoovering the blood through the straw. "I see them."

"See?" Dean asked, confused, until Sam opened his eyes and black bled out from the pupils as Dean watched. "Just kill 'em all," Dean choked. "Get this over with."

In the rearview mirror, the cop stumbled to the ground, glowing from within.

The discussion had gone like this:

"It's a fortress," Sam said.

Dean nodded stiffly. He wiped blood off his chin and almost licked his fingers clean before Sam smacked them away. "Sounds like," he said, hooking his hands in his pockets. "It's gotta be the angels behind this, I mean, who do you think found Cas first?"

"Joint venture," Sam mused. "Demons get Cas so they can lure us in, angels get you, demons get me. And they probably get to keep Cas, plus who knows what other incentives to make sure they give you up at the end of it."

"That's the MO," Dean grunted. "Goddamn kidnappers." He slumped against the wall and glanced at the demon again, which was grunting and moaning around the two cups of salt duck-taped into its mouth. "So," he said with his suicide smile. "Say we Rambo it. Take all the small arms, spare clips, smoke bombs, work our way in, get to Cas. If they got him under some kinda anti-angel mojo, we get rid of that, and he's our exit."

"They'll kill you," Sam said.

"I'm valuable."

"Sure, valuable enough for a couple centuries of angel gang beatings upstairs. We should maybe avoid dying right now."

"Well, if they move him, we lose him. If they see us, the angels will be right there watching—maybe we could take the sewers—"

"It's…possible," Sam said with a wince.

"Don't tell me you forgot about my evil twin?"

"No. Dean—I mean, if it's either a Kamikazi mission, or, well—it depends on what we're willing to do. What if we killed them all before any of them knew what was happening, two minutes later we have Cas, we're getting out of there, and then…dealing with the fallout."

"The fallout," Dean repeated. His eyes widened and he shrank against the wall. "Sam?"

"We can't afford to die," Sam said. "If we want to get Cas out of there and stay out of their hands, I think it's…possible. We owe Cas."

Dean glanced down at his left palm. There was a sigil on it in marker pen, something that wasn't in any demonology book and that he'd never seen topside until he'd drawn it tonight, that could swing pain and fear into a feedback loop that would last as long as he kept his hand on the victim. By demon standards, that shit was for kindergarteners. "If we do this, they don't get you," he announced. "If you don't think up a better plan, I will kick your ass until you need an ice-pack to sit, and if I go along with this, you do the same to me, but they Do. Not. Get you."

Sam nodded shakily. "Safety first."

Note: Canon upstages me! This just goes to show that any time I think there's a line on this show between practicality and acceptability, it's gonna get crossed. I should've caught a clue when John Winchester ordered Dean to break into the nearest funeral home and steal blood from corpses.

Damn, I need to write faster.

Regarding the anticoagulant: blood in Kripke's world seems to be made from corn starch, corn syrup, and red food coloring, which pours well and stores fine at room temperature. The real thing sets up like cheese curds a few minutes after exposure to air, and the smell of rotten blood is a pretty significant component of the smell of rotten corpse. Sam was carrying it around for days without refrigeration. I'd say he cut it with whiskey and ate a lot of mints.

Anyway, to get the blood back out of a milk jug once it's been let stand for an hour or so, they'd have to whisk it vigorously or throw in some heparin beforehand.