Constantinople, May 1453. In the dying days of the Byzantine empire, as 7000 armed men prepare to defend the city against the might of the Ottoman Turks, Isaak Metochites and his family are entrusted with a purple-velvet bundle. Inside is a silver reliquary carved with the figure of a weeping angel and an inscription: Behold the Proof of Chora, Container of the Uncontainable. The treasure within the reliquary must be smuggled out of the city before it is overrun. Four hundred years later, in Istanbul, the local magistrate, Kamil Pasha, is plagued by thefts of antiquities from mosques and churches that appear for sale in Europe within days. In addition, there has been a series of murders in which the bodies all bear the same distinctive markings. Sources lead Kamil to a community living in an abandoned cistern called Sunken Village and to a mysterious sect descended from Abyssinian slaves. Deep within the tunnels under the old city a war is being waged, and the re-emergence of the forgotten reliquary sets off a race for its possession between those sworn to protect it and those who will stop at nothing to exploit the ancient secret contained within.