Anna Lang lost everyone she loved during the Second World War—except her cherished music teacher, Esther Haymann. When Miss Haymann dies under suspicious circumstances and rumors of suicide swirl, Anna doesn't want to believe them. Her doubts intensify when she catches a stranger rifling through Miss Haymann's papers, claiming a link between her death and that of renowned scientist Alan Turing.

Arthur Cavendish, a former prisoner of war in Korea, can't completely escape the nightmares of combat and captivity. Nor can he forget that Dr. Turing's advice once saved his life, so Arthur is determined to get to the bottom of Arthur's associate's alleged suicide, even if it involves trespassing and danger.

When a suspicious fire nearly kills Arthur and Anna, they form a reluctant alliance to clear their mentors' names. From shadowy corners of seaside resorts to the guarded gates of a secret government agency at Hanslope Park, Anna and Arthur chase elusive clues—and wrestle with their growing attraction for each other. With divergent goals and hidden secrets, a future together seems unlikely. Yet as more and more pieces of the puzzle fall into place, a sinister pattern unfolds, and they find that their hearts are not the only things at risk. Uncovering the truth might cost them their lives.