KM Classic The Valley of Fear by Arthur Conan Doyle
The Valley of Fear is the fourth and final Sherlock Holmes novel by Sir Arthur Conan Doyle. The novel starts with Sherlock Holmes receiving a cipher message from Fred Porlock, an agent of Professor Moriarty. After Porlock sends the message, however, he changes his mind for fear of Moriarty's discovering that he is a traitor. He decides not to send the key to the cipher, but he sends Holmes a note telling of this decision.