As India celebrates the arrival of a momentous new decade, Inspector Persis Wadia stands vigil in the basement of Malabar House, home to the city's most unwanted unit of police officers. Six months after joining the force she remains India's first female police detective, mistrusted, sidelined and now consigned to the midnight shift. And so, when the phone rings to report the murder of prominent English diplomat Sir James Herriot, the country's most sensational case falls into her lap.

Hours later, the man’s cold body lies in the city mortuary, alongside the woman he couldn’t save. And his sister, unconventional nurse Gemma Tate, tracks down troubled police inspector Sebastian Bell to unravel the truth. Sebastian has enough pressure to solve the murder of an aristocratic heiress without Gemma meddling in his case. But the cryptic sentences she brings him from her brother’s notebook could be a crucial lead. If only they knew what “milky way” meant.

England. 1923. After a year away at finishing school where she learned etiquette, deportment, and the difference between a fish fork and a salad one, Kitty Worthington is eager to return home. But minutes after she and her brother Ned board the Golden Arrow, the unthinkable happens. A woman with a mysterious connection to her brother is poisoned, and the murderer can only be someone aboard the train. When Scotland Yard hones on Ned as the main suspect, Kitty sets out to investigate.

Istanbul, 1922. Lady Marigold Grey—former British spy and daring adventuress—sets out for England on a luxury train. But where Marigold goes, trouble follows. When the director of the train is murdered—and false evidence linking her to his death emerges—Marigold suddenly finds herself on the fast-track to becoming a prime suspect.

December 1899. After the death of her beloved grandmother, Cleopatra Fox moves into the luxury hotel owned by her estranged uncle in the hopes of putting hardship and loneliness behind her. But the poisoning of a guest on Christmas eve throws her new life, and the hotel, into chaos. Cleo quickly realizes no one can be trusted, not Scotland Yard and especially not the hotel’s charming assistant manager.