"Dean? DEAN!" Sam shook him wildly, but Dean's head only lolled in his arms, completely unresponsive. "DEAN!"

Nothing.

"CAS!" The angel was already there, his trench coat whirling around him as he crouched on Dean's other side. He pressed two fingers to Dean's forehead, closing his eyes and furrowing his brow in concentration. Sam waited, hardly breathing, clutching his brother as though scared he would disappear.

Cas flinched. He withdrew his hand as though he'd been burned, his eyes widening in horror as they gazed down at Dean.

"Cas? Is he –"

"He's alive," he whispered, sounding as though he was delivering far more grim news.

"Then what's – what happened?"

"He's ... I'm not sure, I ... I can't heal him."

"What do you mean you can't heal him? What's wrong with him?"

Cas looked up at Sam. "I ... I can't be sure. His body feels healthy; I can't sense anything that I shouldn't. But he's ... deeply unconscious. Deeply. His breathing is shallow and is heart rate is low."

"Well, what does that mean?" Sam asked, his patience draining as he held his brother to him.

"I don't know, Sam."

"Is he just unconscious 'cause of the cure? He just needs some rest, right? It took a lot out of him."

"Yes, I expect that's true."

Sam sensed a conjunction coming. "But?" he guessed warily.

"But," Cas confirmed, "I can feel something in him. Something ... wrong."

"Cas, if you don't spit it out, I swear I'll –"

"I don't know what it is, Sam!" Cas snapped, exasperated. "It feels like a kind of icy fire. That's the only way I can think to describe it. It just feels wrong, unnatural. But it also feels familiar."

"What do you mean?"

"I think I need to touch Dean's soul. Then I'll be sure."

Sam blinked. "Touch his soul?" His voice sprang up an octave. "What the hell, Cas! Why?"

"Do you remember when you were undertaking the Demon Trials?"

"Yeah, vaguely!"

"Whenever I touched you, I could feel something similar. And when your soul came back from the Pit – it feels like that too."

Sam swallowed hard. A horrible sinking feeling shivered through him. "You think his soul is ... what? Damaged?"

"Yes. Badly."

Sam gulped again. "How bad?"

"I can't know unless I touch it." Cas's eyes were filled with sorrow and – Sam was horrified to see – fear.

Sam thought for a moment. He knew an angel touching a human's soul hurt. But more than that, it was a violation. God, Dean would hate it.

Tough.

"Do it."

Sam maneuvered himself to the side, supporting Dean's shoulders and resting his head against Sam's chest. Digging the key from his pocket, he unlocked the padlock securing the collar and carefully pulled it off his brother's neck. Deep scratches painted Dean's throat a bright red, with darker patches of dried blood layered beneath the fresh. Sam threw the collar away and it clanked against the concrete before scraping to a halt.

Cas was rolling up his sleeve, his face grim. "Hold him still," he ordered. "This will hurt."

Swallowing his fear, Sam wrapped his arms around his brother's chest, pinning him in a tight embrace.

Throwing Sam a determined glance, Cas snaked his fingers into Dean's stomach, just below the ribcage. Dean bucked in Sam's arms, his brow furrowing in pain as Cas sunk his arm in deeper. A dim light shone around Cas's arm, far dimmer than Sam remembered a soul being. Dean jerked again, but still he made no sound. Sam gripped him tighter, screwing his eyes shut, wishing there was a way for him to feel the pain instead.

After a few seconds that passed in an age, Cas withdrew his hand. He looked like he was about to be sick. Bracing his hands on his folded knees, he took several deep breaths.

"Well?" Sam asked timidly, terrified of the answer.

"It's bad."

"Cas." Sam waited until the angel looked up at him. "Tell me."

Closing his eyes for a brief moment, Cas spoke. "Dean is soulsick."

Sam stared. "Soulsick?"

"Yes. It seems the cure ..." Cas heaved a great sigh and looked up at Sam, gathering his thoughts so as to explain the situation to the younger Winchester. "The cure ripped the demon from Dean's soul the way you'd burn away a tattoo – only far more violent. Like pulling catchweed from unspun wool. The demonic taint was scorched away, but it was so integrally woven into and through Dean's soul that they were almost one. So with every speck of demon that got ripped away, a piece of soul was torn from the whole.

"Souls are fragile, but powerful. The threads coalesced, like stars forming: the bigger the fragment, the more smaller pieces of debris it draws into it, making it bigger, stronger. But some of the pieces haven't ... reformed properly. His soul is cracked and severed and more damaged than I thought a soul could be and still endure."

Sam wondered idly how he was still sitting there when the world beneath him had vanished. He felt he should be falling.

"So w-what does that mean?"

Cas met Sam's gaze. "I don't know."

"Will he wake up?"

"It's ... possible."

"Okay, so what do we have to do?"

Cas raised a hand, halting Sam's eagerness. "There's nothing we can do. This, I think, is something only Dean can fix."

Sam stared at his friend hopelessly. "So, what, we just leave him half-alive while he, what, tries to glue his soul back together? Is that even possible?"

"You did it."

Sam blinked. Yes, he had pieced himself back together after his soul was saved from the Pit. And it had almost destroyed him.

He looked down at Dean's lax yet pained features. He had pieced himself together to get back to Dean. He took back the pain of Lucifer's tortures to return to his brother. It had been one of the hardest things he'd ever had to do, which, in his life, was saying something. But he had done it, alone, to get to Dean.

Sam clenched his jaw and jerked his chin down in a decisive nod. If he could claw his way back through that, then so could Dean. Dean would come back to him. He was sure of it.

"So can he," he said down to his brother, his voice sure and strong.

They carried Dean to his bedroom, and, feeling a gut-wrenching sense of dejà vu, Sam laid him gently on the bed. Cas healed his scratched throat while Sam unlaced and removed his boots and pulled a blanket from a closet down the hall and settled it over his brother's still form. After that, there was nothing more they could do for him. Unwilling to leave his side, Sam pulled a chair up and sank into it, leaning his elbows on his knees, watching Dean. He might not be able to help his brother piece his soul back together, but that didn't mean Dean had to be alone in doing it. If the only way Sam could offer any help was to sit by Dean while he fought for his soul, then he wasn't going anywhere.