It is a year of change and upheaval for the entire Potter family. Harry, as head Auror, has been sent to the United States to help investigate a nefarious underground group whose proclaimed goals are to unite the Muggle and magical world by any means necessary. Unwilling to be separated for the lengthy trip, Ginny insists that family accompany Harry, launching a year long journey to the United States and the American wizarding school of Alma Aleron.

Determined to avoid adventure for the term, James finds himself unwittingly pulled into an international incident involving Petra Morganstern, who has accompanied the family to the states along with her younger Muggle step-sister Izabella. Apparently framed for a crime she didn't commit, James, Ralph and Zane must prove Petra's innocence before she is separated from Izzy forever.

Complicating matters, however, is the very real possibility that, despite James' growing feelings for Petra, she may indeed be guilty of the crime she has been accused of, and perhaps even worse things. Because Petra, as James slowly learns, is no ordinary witch. Her magic is mysteriously powerful, even without a wand, and headmaster Merlin himself seems wary of her.

In the end, James must choose to confront the truth that he has been seeking, knowing that it may well shatter his perception of the girl he loves, and even the stability of the magical world at large.