 Jack, after finding out Lucifer murdered Maggie, rejects him, which causes Lucifer to admit he only needs his power, causing him to steal Jack's grace and disappear with him and Sam.Castiel and Dean tell Michael of the situation, who is willing to help them defeat Lucifer, but cannot fight him due to the damage to his vessel.Over the protests of Castiel, Dean tells Michael that he is his true vessel, and that he will be his vessel and they can defeat Lucifer together if Dean remains in control.