Book I, the Secret London, introduces the sisters Calliope and Coi. One is troubled by bad dreams, the other has simply vanished from the world. As Calliope tries to come to terms with the unnatural design of a reoccurring dream, and a man she keeps meeting there, she attempts to convince the waking world her sister is lost but not gone. A variety of characters attempt to offer her advice and council regarding the sudden disappearance of Coi, but it's the ghost in her dreams who ultimately puts her on the path to follow her sister. He reminds her of a story someone close to the sisters once told them and suggests that perhaps Coi took the story a little too much to heart. Upon waking Calliope sets out to follow the same trail her sister set out upon before her and comes to find an unseen doorway that leads her to the secret London. It's there that Calliope realizes that perhaps her dreams aren't really dreams at all...