James Keane, officer in the 27th Foot, card sharp, ladies' man and one of the finest but most rebellious soldiers in the British army, is under threat of court martial for disobeying Wellesley's strict rules. But his special, even ungentlemanly, skills have caught his general's eye, so he is selected to form a unique unit which will work behind enemy lines.

Keane's next task is to hand-pick his band of men, some from prison for their aptitude at lock-picking and forgery as well as fighting skills, and form them into an effective unit before being sent on their first intelligence-gathering special mission, this time to link up with a lethal Spanish guerrilla leader.

Stealing into Oporto, Keane's men have to hold a vital post over the river a crossing against overwhelming forces, before being detached once more into the high mountains on another mission where the strains of the diverse characters of the unit test Keane's leadership skills to the uttermost.