4x20 The Rapture

Castiel appears to Dean in a dream and says he has something important to tell him, but that they need to meet somewhere private. At the meeting spot, however, Sam and Dean find Castiel’s human vessel, Jimmy Novak, instead, who cannot recall what Castiel wanted to tell Dean. The characters speculate that Castiel has been attacked by other angels and dragged back to Heaven, where Anna fears that he will receive a terrible punishment for whatever he found out and wanted to tell Dean. Jimmy tries to return to his family and normal life, despite Dean and Sam's concerns about his and his family's safety. Their fears prove true when demons aim to capture Jimmy by possessing his wife and kidnapping his daughter. Sam, Dean, and Jimmy are captured trying to rescue them and Jimmy is shot. However, Castiel possesses Jimmy's daughter and he and Sam kill the demons. Sam, whose powers are failing from a lack of demon blood, drinks blood from a demon in front of a horrified Dean and Castiel, so that he can exorcise Jimmy's wife. Not wanting his daughter to have to suffer as Castiel's vessel, Jimmy has Castiel possess him once again, but Castiel refuses to tell Dean what he wanted to talk to him about, having learned his "lesson" that he serves Heaven and not humanity and certainly not Dean. Dean and Bobby then trick Sam and lock him in Bobby's panic room to detox from the demon blood which he is now addicted to.