The two eventually begin to come back together as Sam learns more about Abaddon's history and plans after he learns that she has been taking souls while leaving the victims 'alive', much like he was after his escape from Hell. They eventually manage to determine the location of a portal to Heaven that allows Castiel to trap Metatron while Dean kills Abaddon with the First Blade – acquired from Cain himself and the only weapon capable of killing a Knight of Hell – but Castiel is left dying of the grace he stole to regain his powers while Dean is transformed into a demon due to the First Blade's influence.