1098. The armies of the First Crusade race across Asia minor, routing the Turks and reclaiming the land for Christendom. But on the Syrian border, their advance is halted before the impregnable walls of Antioch.

As winter draws on, they are forced to suffer a fruitless, interminable siege, gnawed by famine and tormented by the Turkish defenders. The entire crusade is on the verge of collapse. His lord, the ruthlessly ambitious Bohemond charges Demetrios Askiates to find the killer. But as Demetrios investigates, the trail seems to lead ever deeper into the vipers' nest of jealousy, betrayal and fanaticism which lies at the heart of the crusade.