Rising above the city of Collis is the holy Sanctum. And watching over its spires is Catrin, an orphan girl with unique skills—for she alone can spot the building’s flaws in construction before they turn deadly. But when Catrin witnesses a murderer escaping the scene of his crime, she’s pulled into a dangerous chain of events where the only certainty is that the killer will strike again. Assigned to investigate is the mysterious and brilliant Simon, whose insights into the mind of a predator are frighteningly accurate. As the grisly crimes continue, Catrin finds herself caught between killer and detective while hiding her own secret—a supernatural sight granted by the moon, destined to make her an outcast, and the only thing that might save her and those she loves from becoming the next victims . . .