The man who lies bleeding to death in a London brickyard is no ordinary drifter but a secret informant with details of an international plot against the British government. Special Branch officer Thomas Pitt, hastening to rendezvous with him, arrives seconds after the knife-wielding assassin—who, in turn, flees on an erratic course that leads Pitt in wild pursuit to picturesque St. Malo on the French coast. Meanwhile, Pitt’s supervisor, Victor Narraway, stands accused of embezzling government funds. Since the man who ruined Narraway’s career is in Ireland, Pitt’s clever wife, Charlotte, agrees to pose as Narraway’s sister and accompany him to Dublin to investigate. But unknown to Pitt and Narraway, a shadowy plotter is setting a trap that, once sprung, could destroy not just reputations but the British empire itself.