Cassie and Izzy bundle up and try to use the Book of Doors for a “magical midnight tour of Manhattan,” choosing the Library Hotel’s roof terrace. Cassie fails at first, then realizes she must visualize the specific destination door; as the book grows heavier and glows with a rainbow aura, their apartment door strangely “locks” until Cassie understands the terrace door opens outward and pushes it instead.

They step onto the Library Hotel’s snowy terrace, thrilled by the stormy skyline and the pianist’s music drifting from inside. Cassie marvels at the book’s miracle, while Izzy revels in the moment and pulls Cassie into a brief dance in the snow.

As they talk, Izzy pushes Cassie to consider what the power could enable—crime, invasion, theft—warning that it is “lucky” a good person has it. Cassie resists the dark possibilities but grows eager to keep exploring. They notice a lone man watching them briefly before looking away.

Using the book repeatedly becomes easier: Cassie and Izzy travel through doors to the New York Public Library’s dark reading room, then to the Strand Bookstore, and finally to Ben’s Deli. Over late-night food, Izzy insists Cassie should stop playing with the book until she learns more; Cassie decides she will ask Mrs. Kellner about John Webber.

Back home, Cassie discovers John Webber’s handwritten message has vanished from the book’s front page, leaving only the book’s basic description. Despite the warning and the unsettling change, Cassie uses the book alone, visualizes a hostel door from a past London trip, and opens her bedroom door onto a rainy London street—confirming she can return to doors she remembers, anywhere in the world.