"Say yes Sam," Lucifer's vessel was rotting from the outside in, skin falling off his bones in an alarming way.

"Say yes Sam," his voice was silky, insistent, "say yes or I will cut your brother's throat."

Dean hung in Lucifer's arms. The demons had done a job on him and he was almost too weak to stand. Green eyes stared painfully, swollen mouth trying to make some sounds. Lucifer smiled and held the knife closer to Dean's throat, the blade cutting into soft flesh, blood trickling down ravaged skin.

"Sammy – no!"

Finally Dean got the words out and he tried to lift his hands, pull the clawing fingers away from his body, "Sammy – don't do it."

Sam stood stock still; his eyes blurring, his mouth dry.

There was only one thing he could do in this situation, only one thing he could say. Despite his brother's protests, despite everything, he opened his mouth and begged for forgiveness in his heart.

"Yes," he said, firmly, "yes, yes, yes…"

****

The smell of rot hit Dean immediately as the body behind him fell – lifeless – to the ground.

Sam – or not Sam now – had vanished, gone as if he had never been there and Dean dropped to his knees, vomiting hard, the corpse behind him stinking like the dead thing it was.

Dean wanted to shout, wanted to weep, wanted to scream. He buried his head in his hands and prayed hard, wondering if anyone would hear him, wondering if anyone would come.

The sudden fluttering of wings made him look up. A familiar figure, trench coat filthy now, suit ripped, tie gone. Castiel's blue eyes observed him with some pity and the angel knelt down and put his arms around Dean's shaking shoulders, deliberately ignoring his tears.

"How did you find me," that one sentence, ground out, his energy draining away.

"This is Detroit," Castiel looked sad, he actually looked sorry, "what was prophesised has come to pass – we must leave here."

"No," Dean remembered Zachariah and the things he had seen, the future could be changed, it had to be changed, Dean could not – would not – confront that vision of his brother again, white suit, slicked hair, an expression that Sam would never wear, "no Cas – not without Sam."

The angel did not react, did not deny, just nodded his head – once.

"You must rest first," he said and he touched Dean's forehead gently and Dean knew no more.

****

Dean threw his duffle into the Impala and got behind the wheel. Castiel looked concerned and opened his mouth to speak only to be interrupted by Dean raising his hand.

"No," he said, firmly, "I don't want to frigging hear it Cas – I don't want to hear anything – I have to go and get him back."

"It won't be him," Castiel's face does not crack, it is stoic, expressionless, "you saw what happened to Raphael's vessel – Lucifer is far more powerful – there will be nothing left of the Sam you know Dean – you have to accept that."

Dean said nothing; what was there to say? He swallowed down the lump that seemed lodged in his throat and rubbed at his face.

Why them? Why Sam? Despite everything that had happened in this last, painful year, Dean knew that his little brother was a good man, a great man. He knew that Sam had tried so hard to stop this, that Sam had thought that killing Lilith would be a good thing. He refused to think, to believe that his baby brother would turn evil and he would never, ever put a gun to Sam's head.

Now he tucked the colt – although useless – into his back pocket and Ruby's knife into his belt. He knew he wouldn't use them on Sam – couldn't but it felt good, familiar, to have them and he started up the car and pulled out of the lot.

He had a long way to go…

****

Every so often Dean kept glancing at the passenger seat – heart sinking as he realised it was Cas sitting there not his brother.

Dean bit his lip hard until he tasted salty blood. He missed his brother – he missed Sam and his big, warm presence. They had been apart too much lately, they hadn't been brothers in a while and he missed it, missed the closeness and the prank wars and the familiarity of it.

Now Sam was gone – again – and Dean wasn't sure he was ever going to get him back.

"You will have to kill him," Cas's voice broke through his fug and he shifted in his seat, tired, stiff, so full of grief that it threatened to choke him.

"I can't," Dean had lived in the comfortable world of denial for a long time and he wasn't moving anytime soon, "he is my brother."

"Not any more," Castiel said and Dean wanted to slap him, wanted to stop the car and scream at him, wanted to drive the car into a tree and – maybe – end it all.

"I'm getting him back," Dean said, "whatever is left of him – whatever is left of Sammy – I'm getting him fucking back."

Castiel was silent for a long time and Dean realised that he was holding his breath, waiting for the angel's answer.

"Then I will help you," Castiel said, finally, "because Sam is my friend."

And that – Dean mused – was enough…

TBC