Danny Caulfield's quiet Christmas break from Wilsons, the school for spies, is shattered by gunshots and a heartrending discovery about his parents. That same night, he's summoned to Wilsons' to prepare for a mission: under an assumed identity, Danny must find a way to protect the Treaty Stone that keeps peace between the Upper and Lower worlds. Meanwhile, the evil Ring of Five pursues Danny, for he is the "true Fifth"—only Danny can unite the members of the Ring and awaken their full powers as master spies.