The forever man / Eoin Colfer.

Enhanced descriptions from Syndetics:

Riley, an orphan boy living in Victorian London, has achieved his dream of becoming a renowned magician, the Great Savano. He owes much of his success to Chevie, a seventeen-year-old FBI agent who traveled from the future in a time pod and helped him defeat his murderous master, Albert Garrick. But it is difficult for Riley to enjoy his new life, for he has always believed that Garrick will someday, somehow, return to seek vengeance.

Chevie has assured Riley that Garrick was sucked into a temporal wormhole, never to emerge. The full nature of the wormhole has never been understood, however, and just as a human body will reject an unsuitable transplant, the wormhole eventually spat him out. By the time Garrick makes it back to Victorian London, he has been planning his revenge on Riley for centuries. But even the best-laid plans can go awry, and when the three are tossed once more into the wormhole, they end up in a highly paranoid Puritan village where everything is turned upside down. Chevie is accused of being a witch, Garrick is lauded as the town's protector, and . . . is that a talking dog? Riley will need to rely on his reserve of magic tricks to save Chevie and destroy his former master once and for all.