Castiel has walked through Dean's dreams many times but this is the first time he's had one of his own. The last thing he remembers is sitting behind Dean and Sam in the Impala; he must have..."nodded off," he believes is the term. It's disconcerting.

He's in a familiar room. He walks the length of it, trying to place it in his memory when passes over a spot that makes him shiver. He crouches and sees a charred circle on the floor; he touches it and his fingers sting. Holy oil. Horror floods him; he knows where he is now, the town where Death rose, but as he stands up he knows the realization comes too late. There's a presence behind him, a darkness, and Castiel turns to see Lucifer standing there in his rotting vessel. "Well," Lucifer says, with an appraising look that burns. "Isn't this interesting."

Castiel has time to take a step back before Lucifer grabs him by the collar and hauls him off his feet. "I've never walked through an angel's dream before," Lucifer says. "What an odd feeling." He shoves Castiel against the wall hard enough to drive the breath out of his lungs. Lucifer watches him gasp, a mixture of amusement and actual concern in his red-lined eyes. "You're so weak you actually need to breathe," he marvels. "Oh, Castiel, what have they done to you?"

He feels what little remains of his Grace leap at how Lucifer lilts the last syllable of his name. He's too young to have really known the Morning Star as he was, that being of perfect beauty, but he can't stop himself from being himself drawn to the echo. He closes his eyes. "Let me go."

Lucifer clucks his tongue at him. "This all must be quite terrifying for you," he says, so close that Castiel finally understands Dean's complaints about personal space. "To be so helpless. But that's what comes of helping the humans. They destroy everything, little brother. They're a cancer infesting this beautiful world our Father created."

The smell of decay is overpowering. "You underestimate them. Dean and Sam will defeat you."

"And then what becomes of you?" Lucifer presses one hand to Castiel's chest and it's cold, so cold Castiel's whole body shakes. "I can still feel it, you know. Your Grace, deep inside like a dying ember. But if they win, these little humans you love so much, it will wither until you're no better then they. You'll be trapped forever in this...meat." Lucifer leans close to his ear. "I would rather be back in the Cage." Castiel feels those eyes study him for a moment, then Lucifer tips his chin up. "But don't fret. I can stoke it, little brother. Make you strong again. So strong even the archangels will flinch from you."

And there's a moment, the briefest instant but an eternity to an angel, where Castiel considers it. "No," he says, weighing that promise of power against the revulsion on Dean's face when he found out.

Lucifer smiles. "You'll feel differently once I'm done."

Dean. Dean, wake me up. "I said no." He feels genuine panic for the first time in his existence; Lucifer's grip is too strong to break, he can't fly, he's never dreamed before and he doesn't know how to wake up.

"Shh, shh," Lucifer says, putting one finger across Castiel's lips. "Hush now." He feels his voice die in his throat. "You forget, little brother, you're not actually human. I don't need your permission for anything."

Dean. Sam. He's screaming inside his head, struggling against Lucifer, something that would have been futile even at his full strength. He feels Lucifer's hand press against his forehead. Please. Please, wake me up.

"This will hurt."

Dean.

He jerks awake, gasping and disoriented. "That's it Cas, take it easy. You're all right, you're all right." It takes a few seconds to realize he's still in the backseat of the car, Dean's hand on his shoulder. "Baby's first nightmare, huh?"

Castiel nods. He sags against the seat, shivering with his hands over his face.

"Sucks, don't they." He takes the moment to determine if Dean's making fun of him-he's never entirely sure-but there's nothing but sympathy in Dean's eyes. "Welcome to the human race."

Castiel nods again. It seems the appropriate thing to do. "Thank you."

"Look, Cas, I know how real that must've felt, but it was just a dream, okay? It can't really hurt you."

Castiel smothers the sudden, hysterical urge to laugh-not well enough, he sees the flash of worry in Dean's eyes. "Of course," he says, getting himself back under control. Dean doesn't need to know. He's supposed to ease Dean's burdens, not add to them. In his condition he knows he's already burden enough.

Dean gives him a long, doubting look but doesn't press the issue. "Yeah, well, me and Sammy were about to go on a quick food run. You want anything?"

"I'm fine."

Dean quirks an eyebrow. "You sure? Best burgers in the county. That's what the sign says, anyway."

"Dean. I'm fine."

"Hey, your loss."

He grabs Dean's wrist as he's about to leave. "Don't let me fall asleep again."

Dean's expression softens. "You gotta sleep, Cas. At least it looks that way for the time being."

"It's important."

"How about this: if you do fall asleep again, I'll watch you. Any sign of another nightmare, I'll wake you right up. Promise. Deal?"

He supposes that will have to do. "All right," he says, letting Dean go. He watches Dean run to catch up with Sam until they both pass out of sight, afraid to close his eyes. He still feels Lucifer's hand on his chest, hears Lucifer's voice whispering foul promises into his ear.

He counts every second until Sam and Dean come back.