Quentin receives Julia's apology letter, and he emails an apology back. Julia meets with Richard to discuss how to use magic in a healthy way. He brings her to a patient, Keira, so Julia can use mental projection to heal. She meets Keira in a park in her mind. Keira explains that she learned magic on her own, but she became stuck in her mind for a year. Keira asks Julia to write down a spell she worked out in her mind. Julia reveals that her favorite memory was when she was playing Fillory with Quentin when they were younger. Keira asks Julia to kill her as a favor, which Julia does as part of her redemption.
Quentin is upset that he lost Fillory and Further Book Six, which has all of the answers. He and Alice perform a spell to find it, which leads them to Penny. Penny confesses that he took it, read it, and threw it away. Penny remembers reading that there was a magic button that led Jane Chatwin to Fillory. Quentin thinks that the button could still be in Plover's house in England.
Quentin, Alice, Penny, and Eliot all go to the Plover estate on a tour. Christopher Plover took care of the Chatwin children and wrote the Fillory books. They investigate the writing room at night and find a letter from Prudence, Plover's sister. They realize that Plover was studying traveler magic and probably tried to travel to Fillory. Prudence wanted to cover up the disappearance by saying Plover died.
Alice hears children's voices. The guide catches them, but when the lights flicker, the guide is found dead with his mouth sown shut. Quentin and Eliot enter a restricted room. They see a little boy, George, and they follow him. Eliot and Alice are in a different room tied to chairs with a little girl. The girl warns them about the woman, Prudence. Quentin and Penny realize they're seeing scenes from the past.
In the past, Jane went to Fillory, but Martin was left behind. Jane brought Martin the button, calling it a key. Martin gave it to George to hide. Plover drugged Jane, and took nude pictures of Martin. Prudence killed the housekeeper's children (George and the little girl) for bothering Plover.
Quentin believes that the Beast is Plover, who wanted to learn spells to get to Fillory. They go back to the cellar to retrieve the button from George's pocket. They all go back to the cottage at school. Penny touches the button and disappears.