Here is the Supernatural spoilers: season 5 episode 1 title Sympathy for the Devil that was aired on September 10th.
In this episode Supernatural S05E01, it picks up where they ended the season finale. The last show ended where Sam just opened the gates to hell and Lucifer is coming. The show starts off when Sam and Dean are still in the chapel when a glowing light is blinding them. All of a sudden, they get teleported into an airplane where they are safe.
When the gates were opened, just about every demon from hell is gunning for Dean especially since he’s the only one who can stop Lucifer.
We find out that Castiel is dead and was blown to pieces by an Archangel from being around the prophet.
Everyone is out to find Michael’s sword because that is the weapon that can kill Lucifer. Bobby meets up with Sam and Dean and when he finds out where the sword is, he reveals he was a demon possessed. He build up enough strength to stab myself to get the demon out but then he’s rushed to the hospital.
Later Dean finds out that he’s Michael’s sword from another angel. Well, his vessel and he needs to give permission for Michael, the angel of war, to take over. Dean doesn’t let that happen and he gets tortured by another Angel before Castiel comes back and fights everyone off.
Castiel was dead. He comes back and its said that God brought him back.
Lucifer on the other end is around his vessel and just basically talks his vessel into letting him take over.
At the end of the show, Dean tells Sam that he can’t ever trust him again because what he has become.