Richard Mayhew stumbles upon a girl lying on the sidewalk bleeding. He helps her, and his life is forever changed. She vanishes a few hours later, but the next day no one recognizes him, his bank card won't work and his landlord rents out his apartment. It's as if he's become invisible. He finds himself living in a London most people would never have dreamed of -- a city of monsters and saints, murderers and angels. It is a world that exists in a subterranean labyrinth of sewer canals and abandoned subway stations. It is the home of Door, the girl whom Richard rescued, and whom he must now help in her mission to preserve this strange underworld kingdom from a mysterious figure determined to destroy it -- if he is ever to return home.