Sam tries to figure out what has happened to Dean, who is now a demon running around with Crowley; Castiel faces his diminishing grace.
Crowley notices Dean's increasing level of aggression; a vengeful man named Cole captures and tortures Sam.
Sam works to save Dean from the mark of Cain; Crowley seeks the help of an unexpected ally -- Castiel.
A series of attacks lead to a surprising culprit -- a werewolf named Kate who was left alive by Sam and Dean.
As Sam and Dean investigate a teacher's disappearance, they are stunned to learn that the school is presenting a musical based on their lives.
Dean and Sam go to claim their fortune after discovering that Bobby or his next of kin have been named as a beneficiary in an heiress' will.
Sam and Dean encounter a demon who is running from Crowley, but before they can do anything, Rowena intervenes; Hannah runs into someone from her vessel's past.
Jody Mills (Kim Rhodes) 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.
When Castiel finds Jimmy's daughter in a group home, she persuades him to break her out; Crowley is faced with a big challenge.
In search of a cure for the Mark of Cain, Castiel comes up with an idea that Sam does not support; as Rowena plots against Crowley, Castiel tries to make things right with Claire.
When Sam comes across a video of Charlie attacking a district attorney, Dean thinks she has returned from Oz to hunt on her own.
Sam and Dean tackle a case where people vanish into thin air, leaving only their clothes behind; Dean becomes a victim.
Dean and Sam race to stop a vengeful ghost who has been killing people through various electronic devices.
Sam, Dean and Castiel must deal with Cain's (Timothy Omundson) return; Rowena and Crowley grow closer.
Sam ignores Dean's directive and continues to search for a cure; a new murder case brings the brothers in contact with Cole -- who ends up being infected by a Khan worm that turns men into murderers.
Dean and Sam investigate grisly, identical suicides committed by various people with little in common; the brothers begin to suspect that a priest is involved.
Castiel and Sam pursue a lead about the Mark of Cain; Rowena (Ruth Connell) and Dean have an encounter.
Charlie contacts Sam and Dean after she finds the book of the dead -- which could help eliminate the mark of Cain; Castiel and Metatron look for Castiel's grace.
Sam looks for a magical box built by former Men of Letters, Magnus, hoping it will cure Dean, but is surprised by a deadly alarm system.
Castiel asks Sam and Dean to help Claire find her mother, but when they learn what took the woman, they suspect a happy ending is impossible.
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.
Dean takes matters into his own hands regarding Stynes; Sam attempts to come to terms with his decision.