On a dark, brooding evening on the Isle of Wight, Agnes Raybould and her companion find themselves an empty first-class compartment on the train. But before long a middle-aged man, clearly in high spirits after dining at his club, joins them, and begins a conversation. His name is Edwin Blanchard - and within moments of the train leaving the station, Agnes and her accomplice strangle him .

Detective Inspector Colbeck is called to Scotland Yard immediately and is given details of the violent murder by Tallis. Both Colbeck and Sergeant Leeming are swiftly despatched to Queen Victoria's favourite country home on the island to find out exactly what took place on that dreadful, eery night.