A summer of change brings James Sirius Potter back to Hogwarts School of Witchcraft and Wizardry with a new perspective. Confident that last year's adventures are well behind him, James prepares for the more prosaic challenges of schoolwork, trying-out for the Quidditch team, and keeping an eye on his brother Albus and cousin Rose. A new year brings a new adventure, however, beginning with some increasingly worrisome questions about the new headmaster, Merlinus Ambrosius, whose long trek outside of time may have attracted the attention of a horrible entity known to legend as "the Gatekeeper". Determined to prove Merlin's trustworthiness, James finds himself lost in a deepening web of intrigue, deception and secrets that stretches all the way back to the time of the founders. With the Gatekeeper looming, preparing its prophesied human host for a final reign of doom, James, Rose and Ralph forge unexpected allies in a last-ditch effort to stop it before it is too late. In the end, however, all hopes lead to Merlin, and James must face the very real possibility that everything he believes about the new headmaster is, in fact, a carefully constructed facade.