‘The Valley of Fear‘ is last and the least well-known of Conan Doyle’s four Holmes novels (the others being ‘The Study in Scarlet’, ‘The Sign of the Four’, and ‘The Hound of the Baskervilles’). It features a brief appearance by that Napoleon of crime, Professor Moriarty. We last saw Moriarty some 20 years earlier in the 1893 tale ‘The Final Problem‘, Conan Doyle’s unsuccessful attempt to kill Holmes off.

The novel opens with Holmes receiving an encrypted message from an informer within Moriarty’s criminal network. A follow-up message intending to provide the encryption key instead informs Holmes he has changed his mind, for fear of discovery. Nevertheless Holmes is able to decrypt the message. It is a warning that a murder plan is underway, naming the intended victim, a Mr Douglas of Birlstone Manor. Minutes later, Inspector Macdonald arrives with news that the victim identified in the note has been killed. Holmes deduces this is all Moriarty’s work, but his suspicions are dismissed by the officer.