Autumn 1941. As the war continues and Cambridge endures nightly air raids, its bomb shelters are packed with those driven by the sound of the siren. At dawn, a young man is found dead in a shadowy corner, apparently a suicide, yet Detective Inspector Eden Brooke suspects otherwise: the stranger bears a tropical tan and Brooke's office number on his hand. With police stretched thin over a case of sabotage at a factory making periscopes, fear grips the city. Brooke follows a dark trail to the university, where a laboratory conceals a brutal secret and the key to a wartime killer's deadly game.