It was four in the morning when Dean startled awake.

For a moment he wasn't sure what had woken him; for once it hadn't been a nightmare, because Sam was stirring too. Then the rapping on the door was repeated, and they both turned to look.

They slid out of bed simultaneously, Dean with the Colt in his hand—he'd taken to sleeping with it under his pillow—and Sam opening the bedside table's drawer for Ruby's knife. As Dean's feet hit the floor, the person knocking spoke.

"Dean, Dean are you in there? Please be in there," and they both froze for half a second because it was Cas, only he sounded like he was about to keel over. Dean waved Sam over to stand behind the door and traded him the Colt for the knife. The doorknob rattled. "Dean? It's me, please."

"Cas," Dean said, pitching his voice just loud enough to be heard through the door. "Why aren't you coming in?" It was a damn weird time for Cas to be working out that you couldn't just pop into someone's room.

Cas's reply was confused, and wearily amused in a way that made Dean's stomach twist with an uncomfortable familiarity he couldn't quite pin down. "The door's locked?" Cas said. "Unless you want me to break it. I think I can break it."

Dean threw Sam a glance and saw equal puzzlement on his brother's face—Cas could punch people through brick walls; a motel door shouldn't faze him. They held a brief consultation in their expressions and finally Sam shrugged. Dean agreed with him. "OK, just a sec, I'm opening it," Dean said. He turned the latch and undid the chain, and eased the door open a few inches.

The light over the door cast uneasy shadows on Cas's face, but several things were clear: he was slumped against the doorjamb like he was using it to hold himself up, he was not wearing his suit or coat, and his usual five-o'clock shadow had transmuted itself into most of a week's worth of beard in the roughly ten hours since Dean had seen him last, off on another God-finding expedition. His eyes were fever-bright, pupils shrunk to pinpricks, and when he finally focused on Dean his mouth fell open in obvious shock. "Dean," he said finally, barely more than a whisper. "Oh Father help me, Dean, it's you."

"Uh…yeah," Dean said, and then realized what he was looking at. Sonuvabitch, he thought, in that part of his brain that was always calm. "Come on, Cas, you can't stand out there, it's cold out," he said, marveling at the evenness of his own voice. It was chilly, anyway, and Cas was wearing sandals, light cotton pants and, if Dean was not mistaken, that very same blue shirt. Cas nodded as if Dean had said something profound and said clearly, "You don't need to deal with me getting sick on top of everything else. But I don't get sick, Dean, you know that, I don't…get…" He trailed off, and Dean had to drop the knife to catch him as he folded at the knees.

He dragged Cas over the salt line and the few steps to his bed, letting the man fall in a more-or-less comfortable looking sprawl. Behind him Sam closed and locked the door and flicked on the overhead light. As he turned, his eyebrows practically crawling into his hairline, Sam got his first good look at Cas and froze.

"What the hell?" Sam said.

Dean sighed. "When Zach sent me to the zombie apocalypse," he said. He couldn't seem to tear his eyes away from Cas, who was twitching in his sleep, but he caught Sam's nod out of the corner of his eye. "This is…Cas from then." Sam let out a heavy breath. "He's human, Sam. Not to mention on…basically any drug he could find, as far as I could tell, and the me from the future sent him into a trap to die."

"Human," Sam said, which Dean supposed was really the central point there, not Cas's junkiedom or his own future incredible douchebaggery. "How?"

"He said it happened when the other angels left," Dean said. Sam made a small, surprised noise, but then his face changed to an expression Dean knew far too well; that expression meant Sam was about to say something he didn't think Dean was going to like.

"Dean…are you sure this, well, is Cas?" Sam asked carefully.

"No," Dean said grimly, though he couldn't help but grin a little at Sam's relief. "I think we better run the drill on him. But hey, at least he crossed the salt."

"Yeah," Sam said, and turned to his bag for the silver knife.