It is 1274 and in the fortified city of Acre, the last major stronghold of the Crusaders in Palestine, an epic conflict is beginning.

Will Campbell is a Templar Knight, trained for war, but as a member of the mysterious group known as the Brethren, he is also a man of peace. After years of bloodshed, the Brethren have helped to create a truce between the Christians and Muslims. But Will now fears they have been betrayed. King Edward of England has promised the Pope that he will lead a new Crusade, while in Acre itself, a ruthless cabal of Western merchants, profiteering from slaves and armaments, is plotting to reignite hostilities in the Holy Land.

Meanwhile, in Egypt, Sultan Baybars is caught in a power struggle. His son and heir has become involved in the dangerous designs of the insidious soothsayer, Khadir. While Baybars wants to take on the mighty Mongol empire, Khadir and others want to destroy the Christians once and for all.

As war looms, Will is torn between his oath as a Templar, his secret role in the Brethren and his duty to Elwen, the woman he loves but is forbidden to marry. He is caught at the centre of a web of deception and destruction, as he and all those around him rush headlong towards one of the most dramatic moments in history.