Constantinople, May 1453. In the dying days of the Byzantine Empire, Isaak Metochites and his family are entrusted with a silver reliquary carved with the figure of a weeping angel and the inscription emBehold the Proof of Chora, Container of the Uncontainableem. Four hundred years later, magistrate Kamil Pasha is plagued by thefts of antiquities from mosques and churches and a series of murders in which the bodies bear the same distinctive mark. Sources lead Kamil to a hidden sect descended from Abyssinian slaves living in an abandoned cistern in Istanbul's gritty underworld. The reemergence of the forgotten reliquary sets off a brutal race between those sworn to protect it and those who will stop at nothing to gain its explosive secret.