Bombay, 1857. Jack Lark is living precariously as an officer when his heroic but fraudulent past is discovered by the Devil—Major Ballard, the army's intelligence officer. Ballard is gathering a web of information to defend the British Empire, and he needs a man like Jack on his side. Not far away, in Persia, the Shah is moving against British territory and seeks to conquer the crucial city of Herat. As the British march to war, Jack learns that secrets crucial to the campaign's success are leaking into their enemies' hands. Ballard has brought him to the battlefield to end a spy's deceit. But who is the traitor?