Having returned to Paris from an extended holiday in Corsica, Lord Peter Wimsey receives news that his sister Mary's fiancé, Captain Denis Cathcart, has been found shot dead outside the Wimseys' shooting lodge at Riddlesdale in Yorkshire. His brother, Gerald, Duke of Denver, has been arrested for the murder. Cathcart was killed by a bullet from Denver's revolver, and Denver's only alibi is that he was out for a walk at the time Cathcart died. Lord Peter investigates!