The Vessels

When Dean Winchester is on his deathbed after being torn apart by hell hounds, a demon clearly masquerading as an angel appears and makes him an offer: become its new meat suit, and it will heal his injuries. But things don't go exactly as planned. Despite the assurances that they will share control, Dean wakes up six months later and discovers that the world thinks he's dead.

And the world has changed greatly in time that he has been gone. Sam Winchester has fallen farther and farther out of touch with the hunters he and Dean once regularly chatted with. Angels have stepped into the playing field. And there are rumors that the Devil himself has managed to break free from his cage and walk the earth once more.

As Dean finds himself unable to trust his brother more and more, the only alternative he has is to trust the demon/possible angel sharing his meat suit. Its name?

Castiel.