The Valley of Fear is the fourth and final Sherlock Holmes novel by Sir Arthur Conan Doyle.

Sherlock Holmes receives a message from Fred Porlock, an agent to Professor Moriarty. Moriarty is blameless in the eyes of the law but Holmes knows him to be the controlling brain of the underworld. Together Holmes and Watson decipher Porlocks message as indicating that a man named John Douglas residing at Birlstone is in danger...