At nearly fifteen years of age, Joey Harker learns that he is a Walker, able to travel between dimensions, and soon joins a team of different versions of himself, each from another dimension, to fight the evil forces striving to conquer all the worlds.

It has been two years since Joseph Harker first Walked between dimensions, met the alternate forms of himself, and formed a team to protect the Altiverse in the struggle between the vicious forces of magic and science--and now, injured, he has returned to his own dimension, bringing danger with him.