Somewhere In The Sands of Time, Part the First

SPOILERS for Season 4 before "IKWYDLS"
Then: Fulfilling the contract he made to save his brother, Dean died and was sentenced to Hell. Four months passed. Then Castiel pulled him out and gave him a job. A save-the-cheerleader-save-the-world kinda job. Only Dean's the cheerleader. Coming back hasn't been exactly easy. Sleeping isn't restful and the nightmares won't drown themselves in alcohol. Dean won't say what happened in Hell and Sam won't admit what he did with Ruby while Dean was dead. And how the hell do they stop Lilith from breaking the Seals and prevent the Apocalypse?
Now: Sam wants to learn more about the angels that have saved Dean, why they think Sam is dangerous and just enjoy having his brother back. Dean would like not to have a destiny, not to worry about Sam going dark side and just enjoy other... things for a bit. But investigating the murder of twin sisters reveals a demonic presence and puts the brothers right in the middle of another pair of hunters' cat-and-mouse game. Only these two already know plenty about the angels, the apocalypse, the Seals and why the Winchesters are smack in the middle of it all. And they've got their own mission from God.