S04E20: 'The Rapture'

Following on from last week's revelation, Castiel comes to Dean in a dream and confesses that he has some important information to tell him.

Arriving at the designated meeting spot, the brothers are baffled to find evidence of an angel versus angel battle and a bruised and bloodied Castiel unconscious on the floor.

It soon becomes clear that Castiel has been recalled to heaven - something that only happens in extreme circumstances - and that the man he has been possessing, Jimmy Novak, is now free.

But, matters are soon complicated when Novak ignores the Winchesters' advice that he is in extreme danger and runs away to find his abandoned family, leading him to reflect on why he was chosen to be Castiel's human host.

Elsewhere, Sam resorts to desperate measures after realising that his powers are weakening, forcing Dean to make an unexpected and dramatic decision.