The Books of Magic #4: Consequences (Jablonski, Carla. Books of Magic, #4.)

Do you believe in magic? Timothy Hunter is just like any other thirteen-year-old boy in London . . . except for the tiny fact that he might be the most powerful magician of his time. Tim has decided to finally tell his best friend Molly the truth about his magical destiny. But things get complicated when a familiar visitor from another realm shows up -- someone determined to have his revenge on the great Timothy Hunter, whatever the cost.