Contains spoilers for this episode and earlier episodes.
Stan's secret machine approaches the end of its countdown when federal agents arrest him for stealing radioactive material. Dipper and Mabel initially trust that their great uncle can explain everything, but the investigation reveals false identities and security recordings that undermine his story. Left under guard at the Shack, the twins escape supervision and search for answers with Soos. They uncover the entrance behind the vending machine and descend into a vast laboratory. Stan has been hiding the other journals alongside an enormous device. Reading warnings across the books convinces Dipper that its activation could destroy the universe. The children race to shut it down as gravity disturbances shake the building.
Stan escapes custody during another disturbance and reaches the basement before they can stop the countdown. He begs them to leave the machine running, insisting that his work has been for the family. Dipper cannot accept another unsupported promise after discovering so many lies. Soos restrains Stan to protect the twins, while Mabel is left beside the shutdown button. With everyone floating in the machine's growing force, she looks at Stan and chooses to trust him. The countdown reaches zero, the portal opens, and a stranger steps through. Stan identifies the newcomer as his brother and the author of the journals. The feared destruction does not occur, but the explanation for Stan's hidden life has only just begun.