Holmes and Watson are called to Braddock Castle to investigate the death of Sir Henry Braddock. Sir Henry was found dead in his bed, with a dagger in his heart. There were no signs of a struggle, and the castle was locked from the inside. Holmes and Watson soon discover that Sir Henry was a descendant of the Braddock family, who were cursed by a black guardsman centuries ago. The curse states that every male heir to the Braddock family will die a violent death at the hands of a black guardsman.