God Help the Outcasts

There were few occasions in Castiel's long life when he could ever remember feeling helpless, but after losing his last chance to gain information about the Mark of Cain, the seraph is utterly lost. Desperate to save Dean, he begs his Father for help, and the answer he receives is better than he had ever hoped. Alternate ending to episode 10x10. Angsty Destiel with a happy ending.