Crusade, like Brethren before it, follows Will Campbell, a Templar involved in a secret order known as the Anima Templi, as he tries to secure peace in the Holy Land with the help of Kalawun, a high-ranking officer in the Mamluk court ruled by Sultan Baybars.

Both of these men face plots from within their own organisations to throw the Holy Land into war: in Acre, Will must stop a cabal of merchants seeking to start a war by stealing the Muslim relic known as the Black Stone; while in Egypt, Baybars' son Baraka Khan and soothsayer Khadir al-Mihrani are plotting to overthrow Baybars and redouble the attack on the last remaining Franks in the Holy Land.

Meanwhile, Will's childhood friend, Garin de Lyons, is now in the employ of King Edward I and has returned to Acre to extort money from the Anima Templi and to pursue his own, more selfish ends; and Will faces a threat from Baybars as the sultan gets nearer and nearer to discovering that it was Will who, many years before, ordered an assassination attempt which had failed but had taken the life of Baybars' closest friend.

[3] These sentiments were mirrored by A. Jurek, writing for Curled Up, who stated that "the plot moves swiftly despite complexities and complications exploding on each page.

[5] Andre Delicata, writing for Malta's The Times was a little more critical of the novel, stating that the novel's problem is that "there is simply too much setting with meticulous descriptions where everything is dealt with in equal depth, resulting in a text with several climaxes and anti-climaxes but no real focus.