It is June, 1925. Agatha Christie is holidaying in Cornwall and working on a new novel, a romance. But her plans are interrupted when one of the guests is found shot dead on the hotel tennis courts. Frederick Collyer was researching the life of a local man, an eminent chemist who worked on camouflage. As Agatha is drawn into the investigation, it becomes clear that the killing has its roots in the Great War, and the truth is obscured by the shadows...