In the prologue, the story starts out with Richard Mayhew, an ordinary man with an ordinary job, etc. He gives money to a poor woman, and for free, she reads his future and warns him avoid doors...
Richard Mayhew is going on a date with his fiancée to meet her boss. However, on their way to the restaurant, Richard sees a girl on the street, who is injured and weak. He helps her out, and eventually learns that she is the Lady Door, part of a family that can open or unlock doors that cannot be opened and even make doors open to different places like portals. However, she is the last of the family. The next day, Richard is sent to find the Marquis de Carabas, so that he can help Door escape from two deadly assassins, Mister Croup and Mister Vandemar. Richard brings back the marquis to Door, and together, they disappear. Slowly, Richard's life is starting to split apart. He seems to be invisible to everyone, and sets out to London Below, determined to get his life back. There, he meets Anesthesia, a rat-speaker, that guides him to the Floating Market. She disappears, however, on Night's Bridge, after meeting a bodyguard named "Hunter". Hunter later becomes Door's bodyguard. Now together, Door, Richard, the marquis, and Hunter, they set out for Earl's Court to find directions to the angel Islington because Door's father left his journal and said that Islington could be trusted. However, later, readers find out that the two assassins had made changes to the journal, so that the group would be led to Islington. The marquis leaves because of an old grudge and the Earl gives Door a scroll which includes how to get to Islington. It says that you have to get through Angelus to get to Islington. The Angelus resides in the British Museum. Jessica, Richard's former fiancée, is holding an exhibition that includes the Angelus, and they go to the party and get through Angelus. They meet Islington, and they learn that he was the former angel of Atlantis, but readers learn he let them drown and die and is locked up by Door's family as a punishment. Islington sends them to the Black Friars, who are in possession of the key. This key would unlock his prison and allow him to go to Heaven. Hunter, Door, and Richard face three tests, though Richard passes through the hardest test called the ordeal. He goes insane, though somehow, he manages to survive. The friars give them the key, and they depart. Meanwhile, the marquis hunts down Croup and Vandemar to find information. He is cheated on the deal and is killed. Meanwhile, Hunter, Door, and Richard go to the next Floating Market. They meet Hammersmith and he makes a copy of the key the friars had given them. There, Richard also meets a Velvet, a person who sucks the warmth out of a person, making them die. Richard is the poor victim, though he is saved the marquis, who is resurrected by Old Bailey (he's kind of an important character) because the marquis had given him a silver box with his life in it. They find out Hunter is the traitor and Door is captured by the two assassins. They take her to Islington, whom is the employee of the assassins. Meanwhile, Hunter and Richard battle "the Beast". Richard is the only survivor and is named the "Warrior". He rushes ahead to save Door, but he is captured as well as the marquis. After Richard is tortured, Door agrees to open the door so that Islington can go back to Heaven. However, with the copy of the key and her power, she opens a portal between space and time and Islington with the two assassins are sucked into. Richard, Door, and the marquis are saved by the Black Friars. Since Richard was the one to survive the ordeal, he is the master of the key and decided to go back to London Above. He is overjoyed by it, but later, he wishes to go back to London Below, and the marquis happens to take him back there.
