Guinevere Pettigrew, a middle-aged London governess, finds herself unfairly dismissed from her job. An attempt to gain new employment catapults her into the glamorous world and dizzying social whirl of an American actress and singer, Delysia Lafosse.
During a handover to the head of counter-terrorism of MI5 Harry Pearce, terrorist Adam Qasim escapes from MI5 custody. When Harry disappears soon after, his protégé Will Crombie is tasked with finding out what happened as an impending attack on London looms. Crombie eventually uncovers a deadly conspiracy.