Dean sat against the wall in Bobby's decrepit basement, hunched against the screams of agony coming through the iron door. He knew he was torturing himself, listening to Cas's pain when he had no way to stop it. But he could not make himself move from his spot. His mind was racing, trying to come up with a way to save his friend. In the back of his mind, he already knew. But it was a thought he dared not look at. The very idea froze his body with terror, but he could see no other way. And so he sat in the dark, letting the screams rip him apart.

"Dean." Sam's quiet voice echoed down the hall, confused and concerned. "What are you doing?"

Dean's head snapped up. "Nothing, Sam. I'm just..." he shook his head. "I'm just trying to come up with a plan."

Sam nodded. "I've been thinking about that too." He sighed. "I know neither of us wants to say it, but there's...really only one option. And I'll do it, you shouldn't have to."

Dean looked at Sam, utterly confused. "Sam. What are you talking about?"

Sam sat down beside his brother. "He's been a really good friend to us, Dean. I mean…he gave up a lot for us. He shouldn't have to suffer. I figure, Ruby's knife, if I do it right, it should be pretty painless..."

Dean leaped to his feet, backing away from his brother. "You want to kill him?" His mind reeled at the thought, even though he'd considered it himself countless times. "Then what was this all for?" It was the only argument he could think of. "Then what was the POINT of everything we just went through?!" He passed a hand over his face, then let out a laugh. "Besides, the knife doesn't work. I tried that within the first minute I met him."

"He's not an angel, anymore, Dean! Don't you get it? He's becoming a demon! And you're just going to let him live with that?!" Sam looked at him imploringly. "He doesn't want to live with that. Why force him to for your own selfish guilt?"

Dean set his jaw. "I just cut his wings off, so that he would live. I'm absolutely not going to let you kill him." He held Sam's gaze. "There's another way. The only way. And I'm going to take it."

Sam stared at him. "You don't mean...Dean, you cannot honestly be thinking of saying yes!"

Dean let his breath out slowly and nodded. "Yeah, Sammy, I am. What other choice is there?"

"Dean, no. No way, you can't! Look, I understand that you feel really bad about this, I get it. But you can't just let yourself get angel-whammied into something you don't want to be!"

Dean turned his back to Sam and began climbing the stairs. "Come on, Sam. We need to summon Zachariah." He looked back over his shoulder. "Sam...I'm sorry. I really am. But it's my fault that Cas is dying. All I can do is give myself up."

"It sucks that he's dying, Dean, it does, but honestly? I don't care. We need you more, I need you, not some fucking angel using your body. I need my brother, Dean." Sam's eyes were big, frightened. He stared at Dean, his entire body begging him not to go.

Dean glared. "Cas had saved you, saved us, so many times. And you're willing to just let him go?" He stepped back closer to his brother. "We owe him. I owe him. I don't want to be used as a vessel." He closed his eyes. "I really don't. But it's all I can do for him." He locked his gaze on Sam. "And it's the least I would do for you."

Sam stared at him, speechless, before looking away from his brother, to the iron door. "Does he know?"

Dean sighed. "Know what, Sammy?"

"What you're planning to do. Who you're planning to call."

Dean gave him a weak smirk. "What do you think? Of course he doesn't know." He headed up the stairs again. "I gotta call Zachariah. I want to do this before I lose my nerve."

Sam shook his head. "Dean, I can't. I can't come with you. Not, not to do this."

Dean's shoulders tightened. "I..." He shook his head and turned away. "Fine."

"You don't have to do this." Sam tried one last time.

Dean's only answer was the basement door slamming behind him.

~*~*~*~*~*~

Dean pulled the Impala over to the side of the road and shut off the ignition. There was nothing but empty fields all around him, extending for acres. There would be no one near to witness. He stepped out and walked to the center of one of the fields, forcing himself to take deep breaths. The night was frigid, and his breath left white puffs in the air. Moonlight shimmered on the frost on the ground, which crunched underneath him as he turned to look around him.

"Zachariah!" he yelled. "You're getting what you wanted, you bastard." He turned on the spot, looking around for signs of life. "Come on! I know you can hear me! Zachariah!"

"You presume to call on me, Dean Winchester, after all you have done?" Zachariah appeared, glaring hot daggers. "I should kill you where you stand."

Dean smirked. "But you won't."

"What do you want, boy?"

Dean grit his teeth, forcing the words out, all his instincts screaming against him. "I'm here...to...to make a deal."

Zachariah shook his head. "The angels don't make deals, Dean. Only demons have that trick up their sleeve. However, if you offer something, freely, we might be able to come to a reconciliation."

"Same story, different wording." Dean shrugged it off. "Look. You know...what I did. To Cas." He locked his eyes on the ground. "And so you must know what's happening to him right now."

Zachariah blinked. "I do, yes. I assumed you'd kill him once you knew."

Dean tensed, keeping his eyes on the ground. "No. I didn't."

"Then what could you possibly want from me? Your brother already keeps a pet demon, why not you?"

Dean balled his hands into fists and took a step towards the infuriating angel. "Deep breaths." he reminded himself. "Calm." He forced himself to relax. "I want you to save him." He stared at Zachariah, anger in his expression. "I want you to save him, and in return, you get me."

The angel stared at him. "What are you telling me? You want me to save Castiel's life, and in exchange you will...embrace your destiny? Become the Michael sword?" His eyes narrowed. "Why?"

"Because it's my fault that he's changing. I did this to him." Dean dug his fingernails into his palms, trying to control his emotions. "It's my fault, and I'll do whatever it takes to fix my mistakes." He took a breath, then forced out the word.

"Please."

"I removed your brother's lungs. I threatened you with the pain of a living death. And you did not sway. And now? Now, you say yes?" Zachariah turned away. "I do not believe you."

Fear shot through Dean, terror that Zachariah would really say no. "I swear it's the truth. I'm giving myself to Michael, if you'll only save Cas." He considered falling to his knees, but his stomach rolled at the thought. He settled for begging again. "Zachariah. Please."

"You're serious." Zachariah stared at him, incredulous for a moment, before going back to his usual cold stare. "I cannot return Castiel to his former self. His wings are gone, he cannot be celestial."

Dean choked down a cry of despair, refusing to let the hated angel see his agony. "Then do whatever you can."

"I can make him human."

Dean looked up at him. He hesitated, considering the options, weighing the consequences. Cas would live. He would be mortal, but that was better than demon. And he, Dean, would have to give up his life, his body, everything he had.

"Do it."