Just months after the closure of the Chicago World's Fair, librarian Lydia Bancroft finds herself fascinated by a mysterious dark-haired patron. He has never given her his name, all she knows is that he loves books as much as she does. Only when he rescues her in the lobby of the Hartman Hotel does she discover that his name is Sebastian Marks, that he lives at the top of the hotel, and that most everyone in Chicago is intrigued by him. The two form a fragile friendship, but when she discovers that he is the proprietor of an infamous saloon and gambling club, she is shocked. Lydia insists on visiting the club one fateful night and is suddenly a suspect in a murder. Is Sebastian everything her heart believes him to be?