Contains spoilers for this episode and earlier episodes.
Gideon takes over the Mystery Shack and announces plans to replace it with Gideonland. The Pines family stays with Soos's grandmother, but Stan cannot persuade the town that its beloved psychic stole his business. With no way to support the twins, he decides to send them home. Dipper and Mabel try recruiting the gnomes against Gideon, only for him to turn the creatures on them and steal Dipper's journal. Gideon realizes that it is the third volume and assumes Dipper also knows where the first is hidden. He pursues the twins' departing bus in a giant robot, determined to capture the missing information.
Dipper loses confidence without his journal, but jumps into the robot when Gideon seizes Mabel. He fights Gideon inside its control harness and makes the machine strike itself, sending it off the bridge. Mabel's grappling hook saves both twins. Stan arrives with evidence that Gideon's souvenir pins contain cameras, explaining his supposedly psychic knowledge and the feedback in Stan's hearing aid. The town turns against Gideon, who is arrested, and Stan regains the Shack. Dipper shows Stan his recovered journal, though Stan dismisses its contents as fantasy. Once the children are asleep, Stan takes the journals into the hidden laboratory beneath the house. With all three volumes together, he finally has the instructions needed to start his mysterious machine.