Rising above the city of Collis is the holy Sanctum. And watching over its spires is Catrin, an orphan 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 the web of a dangerous man who will definitely strike again. Assigned to capture the culprit is the mysterious, brilliant, and enigmatic Simon, whose insights into the mind of a killer are frighteningly accurate.

As the grisly crimes continue, Catrin finds herself caught between murderer 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.