Cassie refuses Drummond Fox’s suggestion to destroy or sell the Book of Doors, insisting it was a gift and that it belongs with her. Drummond argues the book is dangerous to more than just Cassie and Izzy, but agrees to focus first on their immediate problem: the threatening man at the deli and the wider pursuit. Drummond says they must return to New York to take steps that will help them.

Using the Book of Doors, Cassie takes Drummond and Izzy from Lyon through an alley door to Cassie’s New York bedroom in the middle of the night. In the apartment, Drummond says he has two objectives: show them the second book he carries, and demonstrate what the Book of Doors is truly capable of. He hands Izzy a light-gray book and identifies it as the Book of Memories, which can strengthen memory or erase it.

Drummond explains he once used the Book of Memories to briefly restore clarity to a dementia sufferer, but the aftermath was “harrowing,” and he has since seen the book used more often to make people forget—sometimes benevolently, often for manipulation, crime, or secrecy. Cassie questions how that helps against Dr. Barbary, and Drummond admits it does not; instead, he says it will help Izzy.

As Izzy holds the Book of Memories, colored lights swirl from it and she begins to feel strange and frightened. Drummond reveals his intent: when Izzy lets go, she will forget the Book of Doors and everything that has happened in recent days, leaving those memories clouded and inaccessible. Cassie protests and tries to stop him, but Drummond insists it is already set in motion and argues that hunters like Dr. Barbary will keep coming; Izzy’s safety requires ignorance.

Izzy begs not to forget, curses Drummond, and asks if the effect can be undone; Drummond says he does not know, and questions why she would want the danger back. Cassie apologizes for blaming Izzy about the online search and promises she will help Izzy remember “once it’s safe.” When Izzy finally loses her grip on the book, she collapses into sleep, confused for a moment beforehand. Cassie slaps Drummond and condemns him for violating Izzy’s mind, then helps carry Izzy to bed.

Afterward, Drummond admits he hated misleading them but claims he does terrible things to protect people, and reiterates that the best way to keep Izzy safe is for Cassie and Drummond—and the books—to leave. He then offers Cassie a next step: he has a place to take her that will explain why this matters, and he offers to tell his story. Drummond asks Cassie if, shown a photograph of a door, she can take them to his library.