London, England, on the eve of World War II. Guinevere Pettigrew, a strict governess who is unable to keep a job, is fired again. Lost in the hostile city, a series of fortunate circumstances lead her to meet Delysia LaFosse, a glamorous and dazzling American jazz singer whose life is a chaos ruled by indecision, a continuous battle between love and fame.

During a handover to the head of counter-terrorism of MI5, Harry Pearce, a terrorist escapes custody. When Harry disappears soon after, his protégé is tasked with finding out what happened as an impending attack on London looms, and eventually uncovers a deadly conspiracy.

Alex Corvis, a man wrongly executed for the murder of his girlfriend, returns from the dead and sets out to find the real killer.