Let It Bleed (2011)

Bobby tells Dean and Sam that Castiel has stolen the Moishe Campbell Diary, but he has a copy. They read the journal and discover that in 1937, H.P. Lovecraft had opened a gate to Purgatory with five worshipers of the devil. Meanwhile Crowley abducts Lisa and Ben to force Dean and Sam to step back. Sam summons Balthazar for help and the angel is surprised by the revelations of the partnership of Castiel with Crowley. While the boys seek out Lisa and Ben, Bobby investigates what happened on 10 March 1937 and discovers the truth about his friend Ellie. Balthazar brings the brothers to an angel-proofed warehouse where Lisa and Ben are held captive. When Dean reaches them, he discovers that Lisa is possessed by a demon.