 After helping the Winchesters fake their deaths to escape the secret service, Castiel attempts to find Lucifer's child, but is convinced to spare the unborn child by his mother, Kelly, who is certain that the baby will be good.When Lucifer returns- Crowley faked banishing Lucifer when in reality he attempted to trap Lucifer in his old vessel and control him- the Winchesters are able to trap Lucifer in an alternate universe where the apocalypse took place as Dean and Sam were never born, but Lucifer kills Crowley and Castiel and takes Mary to the other world with him.Although Castiel is dead, Jack, Lucifer's son, who regards Castiel as his guardian, is able to make Castiel 'wake up' in the Empty, the place where angels and demons go when they die.