The Valley of Fear (Version 3) - Sir Arthur Conan Doyle

Receiving a mysterious cypher message from a Fred Porlock, apparent agent of the infamous Professor Moriarty, Holmes and Watson set about deciphering the message, taking them into the mysterious murder of John Douglas. The connection between the murder and the message from Porlock creates the basis for this new Sherlock mystery, the last novel written by Doyle featuring the famous detective. - Summary by David Clarke