A cipher message, a murder at a moated manor house in Sussex with the victim's face destroyed by a shotgun, and then - halfway through - the book stops and goes to a Pennsylvania coal valley, where a secret society runs the mines by terror. Conan Doyle took the second half from the real Molly Maguires and the Pinkerton who broke them; this is the last Holmes novel, and the two halves are one story.
