Dean is a demon and running amok with Crowley while Sam tries to figure out what happened to his brother. Meanwhile, Castiel is dealing with his diminishing grace.
Crowley is worried about Dean getting out of control, giving him a target to feed the mark. Sam struggles to escape from Cole. Hannah tries to convince Metatron to give Castiel's grace back.
Sam continues to try to save Dean from the Mark of Cain. Realizing that Dean's antics are causing problems for him in hell, Crowley seeks help from a reluctant Castiel.
Jody Mills is matched with an overeager partner during a mandatory sheriff's retreat; when a gruesome corpse is discovered, Jody calls Sam and Dean to help investigate.
Sam and Dean try to deal with the aftermath following the bloodbath. Castiel attempts to fix a struggling relationship with Claire, and Claire wants revenge on Dean for what he did to her friend.
To take his mind off of the Mark of Cain, Dean goes hunting. They track down a ghost that is killing college students through electronics and the internet.
Despite Dean's directive to forget about looking for a cure for the MOC, Sam continues to do research. Dean suspects Sam is hiding something but decides to focus on a murder case where they run into Cole.
Charlie contacts Sam and Dean after she finds the Book of the Damned - which could help eliminate the mark of Cain; Castiel and Metatron look for Castiel's grace.
While investigating a strange murder, Sam and Dean discover the killer has the same tattoo as those from the Styne family; Castiel plays referee when Charlie and Rowena must work together; Crowley turns to an old enemy for help with Rowena.