Supernatural (Season 6)

 The sixth season begins a year after the conclusion of the fifth season, with Dean living a somewhat happy life with Lisa and Ben. When an emotionless Sam returns to Dean, he is forced to leave his new life behind and work with his resurrected grandfather Samuel to capture Alpha monsters for the demon Crowley. The brothers are unable to get much help from Castiel since his time is occupied by a civil war raging in heaven against the archangel Raphael, and they cannot trust Samuel. Dean's suspicions are confirmed when he finds Samuel working with demons to discover the location of Purgatory. Dean discovers that Sam's soul is still in the Cage, so he implores the Horseman Death to retrieve it. To ensure Sam does not remember his time in the Cage, Death blocks that part of Sam's memory using a mental wall. The season's second half revolves around the so-called Mother of All, which ultimately leads to events which prove that Castiel is behind the circumstances of Sam's return, the hunt for the Alpha monsters, and the search for Purgatory and was working with Crowley the entire time. When the brothers try to stop Castiel, he brings Sam's memory of the Cage back and proceeds with his plan, absorbing all the souls from Purgatory and pronouncing himself God, having ascended beyond a mere angel.