Cassie Andrews, a bookseller at an independent bookshop in New York, is chatting with a regular customer, an elderly man named Mr. Webber. They talk about their past travels, and Mr. Webber tells her an embarrassing story from his trip. Cassie pretends she hasn’t heard it before. He encourages her to explore and live life to its fullest. Cassie goes off into the shop, and when she returns, Mr. Webber has passed away. Later, Cassie talks to the police about his death and finishes closing the shop. She discovers that Mr. Webber has left her an unexpected gift: a book titled The Book of Doors and a note.

Cassie goes home to the apartment she shares with her best friend Izzy. They met when Izzy was also working at the bookshop, though she’s since moved into selling fine jewelry. Cassie tells Izzy about Mr. Webber and shows her the mysterious book. They begin playing the “favourite game,” in which they talk about their favorite things. Cassie shares her favorite memory of traveling to Venice. Soon, Cassie gets up; when she opens the door to her room, she finds herself faced with a Venetian street.