The Valley of Fear

The Valley of Fear, the fourth and final Sherlock Holmes novel by Sir Arthur Conan Doyle. Based loosely on the real-life exploits of the Molly Maguires and Pinkerton agent James McParland.
Holmes decodes a cipher warning from Moriarty's organization for "Douglas" in "Birlstone", but a corpse is there already. When Mr. Douglas blows the head off his American assassin, he dresses the body as himself, and hides, to throw off the chase for good. Holmes guesses the missing dumb-bell weighted down the killer's clothes in the moat.