Christopher Chant lives with his mother and father, though he hardly ever sees his dad. His parent's relationship is strained, and they often communicate with each other only through notes to servants or butlers. Christopher is a powerful enchanter, though he does not know it yet.

He often has dreams where he travels to other worlds, and in these dreams the things people give him he can bring back home. When his uncle discovers this, he begins to ask Christopher to perform "experiments" to bring more things back from these other worlds. Christopher helps his uncle first get a cat from a Temple on world 10. Christopher ends up making a deal with the Goddess who lives at the temple of one of the cats for books from his world.

He is seen in the temple and while attempting to flee is run through with a spear. He wakes up in his world with the cat, but he trips and the curtain rod spears him. He survives, and after a few days heals. He goes off to school where he forgets about the experiments with his uncle. When he remembers, he begins going out regularly, to many different worlds, and bring back various things he doesn't recognize.

One day at school he gets hit in the head with a bat and he wakes up in the morgue. Chrestomanci comes to see Christopher but finds Christopher sleeping and doesn't realize he has nine lives (the others were off at other worlds). Christopher's father doesn't give up, however, and sends him to a different magician who discovers silver was preventing Christopher from working magic.

Christopher goes to live with Chrestomanci to be trained to become the next Chrestomanci. He dislikes the experience, and begins to spend more time travelling to worlds and helping his Uncle. He visits the Goddess several times, and gives her books that she absolutely loves to read about a school girl named Millie.

Christopher loses several more lives, and he realizes that if he dies in another world, he will end up dying in a similar way in his world. He also begins to realize that Chrestomanci is trying to find a group of smugglers who were bringing illegal goods to their world. The Goddess discovers she will be killed when a new goddess is found, so she takes one of Christopher's lives and escapes to Chrestomanci castle, where Christopher hides her.

Tacroy (who worked with Christopher in the other worlds) is captured and interrogated about the smuggling, but he remains loyal to Christopher. He is a double agent, so all the others knew him already. Chrestomanci and the others go to attack the Wraith (Christopher's uncle), but they are beaten and Chrestomanci's lives are scattered. Christopher takes over as Chrestomanci. He is able to set up a trap to keep his Uncle from returning with Throgmorten's (the cat form the Temple) and Millie's (the Goddess) help.

Christopher goes with Tacroy and Millie to world eleven, where Chrestomanci's lives are gathered. They are able to get them, but Christopher must sacrifice another life. Back at the castle, they capture the Wraith. The book ends with a note from his parents revealing they met up again and are living happily together.