After a decade of war, the kingdoms of Avendell and Istellia have finally agreed to peace. As nobles and magic wielders from both countries arrive at remote Castle Avendell for a historic all-night masquerade to celebrate, King Costis summons an unlikely group to his chambers: the crown prince, his Istellian bride-to-be, his personal guard, a wild beast tamer, and the palace’s questionable new healer.

But before Costis can reveal why he has gathered them, the castle goes dark. When the lights come back, the king is dead—murdered with the princess’s knife, in a weak spot only his guard knew of, and with venom from one of the beast tamer’s monsters lacing the blade. With no clear killer—and everyone a suspect—they make a risky pact: tell no one until the treaty is signed.

But when a winter storm seals everyone inside and someone aware of the king's untimely death begins to pick off guests one by one, the six suspects must work together to discover who killed the king . . . before one of them is next.