Thomas of Hookton is a seasoned veteran of King Edward's army and a natural leader in what will be remembered as the Hundred Years' War. Accompanied by a small but able band of soldiers, Thomas is sent to Gascony to capture the castle of Astarac. But he has ulterior motives for accepting the charge: Gascony is the home of the black knight -- Guy de Vexille -- who brutally slaughtered his father. It is also reputed to be the place where the Grail was last seen.

While capturing Astarac, Thomas learns of a tragedy in the making: a beautiful young woman named Genevieve, innocent if not pious, is to be burned as a heretic. Thomas prevents the corrupt local priest from carrying out his "God -- given" duty -- a sacrilege that turns him into an outcast, even among his own men. Eventually he and Genevieve have no choice but to flee. While hidden away at a monastery, they learn of a plot involving the creation of an imitation Grail for a diabolical end; and they witness the murder of a trusted priest at the hands of Guy de Vexille.

At last reconciled with his allies, Thomas leads his brave band in a bloody battle to the death, the outcome of which could determine the seat of power -- and the direction of Christendom -- forevermore.