As the aristocratic De Qutteville family prepares for a Civil war reenactment battle, elderly Bentham De Quetteville falls to his death from a roof after seeing a headless horseman. The family legend is that this is the ghost of ancestor Sir Geoffrey De Quetteville whose appearance spells death to those who encounter him. Reasonable Toby De Quetteville's first wife died after an apparent meeting with the spectre, a fact which traumatised his son Simon. Barnaby is sceptical until Toby's unpleasant twin Julian also dies after seeing the horseman. Toby's ambitious wife Betty, who will become lady of the manor if her father-in-law Ludo also dies, becomes a prime suspect, as do neighbouring couple the Fleetwoods, long involved in a land dispute with the De Quettevilles. Barnaby must decide which of them, or any other family member is committing murder whilst perpetuating the myth of the dark rider.
—don @ minifie-1