An impossible crime has occurred. A Treasury officer has disappeared into thin air - vanishing from a building whose entrances and exits are all sealed. To solve the case, the Empire calls on its most brilliant and mercurial detective, Ana Dolabra, and her bemused assistant Dinos Kol.

Ana soon discovers they are investigating not a disappearance but a murder - and one of surpassing cunning, carried out by an opponent who can pass through warded doors like a ghost.

Din has seen his superior solve impossible cases before. But as the death toll grows and their quarry predicts each of their moves with uncanny foresight, he fears she has at last met an enemy she can't defeat . . .