In 1952, four women who worked at the wartime code-breaking centre, Bletchley Park, reunite to track down a serial killer.

During WWII, men and women working at Bletchley Park played a vital role, breaking the codes used by the German military. Nine years later, former codebreaker Susan is a housewife and mother, but she continues to recognize patterns that surround her in everyday life. When a series of women are brutally murdered around London, Susan sees a pattern emerging. However, when a police-search for what Susan believes to be an overlooked victim turns up nothing, she realizes she cannot solve this puzzle alone. Enlisting three former Bletchley Park colleagues: Millie, Lucy, and Jean; Susan knows they have little time to break this code before the killer strikes again.—L. Hamre