Contains spoilers for this episode and earlier episodes.
Gideon wants the deed to the Mystery Shack, but cannot open Stan's safe. He summons Bill Cipher and makes a bargain: the dream demon will enter Stan's mind and steal the combination. Dipper, Mabel and Soos use a spell from the journal to follow him into Stan's memories. Their search is complicated by the strange rules of the mindscape and Bill's ability to deceive them. Dipper opens a memory in which Stan appears to call him weak and worthless. Hurt by what he hears, he pulls away from the others just as they need to stop Bill reaching Gideon with the code.
Bill disguises himself as Soos and tricks the group into finding the combination for him. Mabel destroys it before he can pass it on, provoking a violent attack. Dipper returns to the troubling memory and hears the rest: Stan was describing insults from his own childhood and explaining that he pushes Dipper because he wants him to defend himself. Encouraged, Dipper learns that imagination can reshape the mindscape. He rejoins Mabel and Soos, helping them drive Bill away with creations of their own. Bill leaves with a warning that their paths will cross again. Waking up, they find that Gideon has simply blasted open the safe. Their success against Bill has failed to stop him taking the deed and throwing the family out.