The Earl of Lithorn is a very skilled rider, who nevertheless one day gets thrown by his horse and breaks his neck. Meanwhile, his daughter and heiress claims to have seen a corpse in the library with its throat slit. Is she hallucinating, or is there some deeper mystery that also extends to the death of the Earl? John Mannering (aka 'The Baron') investigates and is soon embroiled in a case that involves not just murder, but espionage and very real danger to himself.