In Ogden, Utah, several angels have been slaughtered for refusing to join Metatron, who claims he can get them back into Heaven. Several angels want Castiel to lead them against him, but Castiel refuses. Castiel is approached by Gabriel, who says he survived and came out of hiding to be the leader against Metatron. Castiel realizes this is an illusion created by Metatron. Metatron views the whole angel war as a story and wants Castiel to play the villain by leading angels against him. Metatron claims that Castiel will fail, but he will let him back into Heaven and give him a power supply for his new grace which will otherwise soon kill him. Sam and Dean capture Gadreel, and while Dean is alone with him, Gadreel goads him about what Sam really thinks of him. Dean is heavily tempted by the Mark of Cain to kill him, but is just barely able to resist the urge. Metatron tells Sam he will trade Castiel for Gadreel. At the trade, Metatron easily puts out holy fire and erases angel warding. He says Sam and Dean cannot stop him, but it will be fun watching them try, as he departs with Gadreel. Castiel seems to somberly accept the mantle of leader of a group of angels as Metatron had wanted.
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"None of it was real but all of it was true" - I like that line! Works for The OA too. I love the love of stories and story telling.