 As Holmes and Watson are discussing a newspaper account of the recent murder of Squire Douglas, a message comes from the inspector in charge of the case, asking for Holmes s help. They travel to Sussex, and visit the castle where the crime occurred. The murder was committed with an unusual weapon, a sawed-off shotgun made in Pennsylvania, in the USA. When Douglas was shot, the castle was sealed up, and there seem to be only two possible suspects. But Holmes quickly realizes that the situation is more complicated than it looks.