Castiel, an angel of the lord, has a mission. He needs to get into Hell. The fate of the world is depending on him. Dean Winchester is in the pit, it is up to Castiel to save him before a demon, Alistair, takes him as an apprentice and breaks the first seal to release Lucifer. He seeks the help of a cross roads demon, Crowley, that has his sights set on the black throne when the apocalypse starts. He must fight demons in home territory, and save Michael's vessel, all without coming face to face with Satan himself.
Dean Winchester opens his eyes and he's a demon. Taking place after the season finale, Dean Winchester sees the world in a darker view. Things seem to get better when he allies with Crowley and uses his new powers to his advantage. Castiel seems to accept him. Dean has a rude awakening when he has to prove to a Hunter that he's still himself. When his family sees things take a turn for the worst, he has to become human. When their attempts fail, Dean must hold onto his emotions. The only way to do so, he learns, is to use the love for his family and maybe even someone truly remarkable that was right in front of him. That is if Sam and Cas find him before someone causes Dean to lose it.