In 1916, the world is at war and the energetic Lady Montfort has persuaded her husband to offer his family’s dower house to the War Office as an auxiliary hospital for officers recovering from shell-shock. Despite the hospital’s success, the farming community of Haversham does not approve of a country-house hospital for men they consider to be cowards. When Captain Sir Evelyn Bray, one of the patients, is found lying face down in the vegetable garden with his head bashed in, both Lady Montfort and her housekeeper, Mrs. Jackson, have every reason to fear that the War Office will close their hospital. Once again, the two women unite their diverse talents to discover who would have reason to murder a war hero suffering from amnesia.

When Mrs. Jackson receives a visit from a cook who believes she was an indirect witness to murder from a poisoned dish of breakfast kedgeree, Lady Montfort promises to do what she can to clear the cook's name. She contrives an invitation to Hyde Castle, the home of a self-made millionaire, to investigate a murder of concealed passions and secret desires. With the help of the invaluable Jackson, Lady Montfort sets about solving the puzzle surrounding the death of the rose society's most popular member and discovers a villain of audacious cunning among a group of mild-mannered, amateur rose-breeders.

Lady Montfort has been planning her annual summer costume ball for months with scrupulous care. But when her husband's degenerate nephew is found murdered, it's more than the ball that’s ruined. In fact, Lady Montfort fears that the official police enquiry is pointing towards her son as a potential suspect. Taking matters into her own hands, she enlists the help of her pragmatic housekeeper, Mrs. Jackson, to investigate the case, track down the women who vanished the night of the murder, and clear her son's name.