Receiving a mysterious cypher message from a <b>Fred Porlock</b>, apparent agent of the infamous <b>Professor Moriarty</b>, <b>Sherlock Holmes</b> and <b>Dr. Watson</b> 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 <b>Sherlock</b> mystery, the last novel written by Doyle featuring the <b>famous detective</b>.