1866. On a dark, brooding summer's evening, Agnes Lenham seats herself in an empty first-class compartment on the train to Portsmouth. She is joined by a naval officer and a middle-aged man, in high spirits after dining at his club, travelling to his home on the Isle of Wight. His name is Giles Blanchard - and within moments of the train leaving the station, the sailor strangles him... At Scotland Yard, Detective Inspector Colbeck and Sergeant Leeming are called to Superintendent Tallis's office, and given details of the violent murder. Their investigation will take them all the way to Osborne House, Queen Victoria's favourite country home, to find out exactly what took place on that dreadful, eerie night.