In 1866, Giles Blanchard shares a Portsmouth-bound railway compartment with an elegant woman who steals papers suitable for blackmail. She leaves the train safely; Blanchard never reaches his home on the Isle of Wight and is found to have been murdered during the journey.
Colbeck and Leeming follow the stolen material through a network of private scandal and deception. Queen Victoria is preparing to spend the summer on the island, increasing pressure for a rapid solution when the investigation approaches a royal residence.