The Valley of Fear

Sherlock Holmes receives a cipher message from Fred Porlock, an agent of Professor Moriarty. However, Porlock changes his mind for fear of Moriarty's discovering that he is a traitor and he decides not to send the key to the cipher, but he sends Holmes a note telling of this decision. From the cipher message and the second note, Holmes is able to deduce that it is a book-cipher. Holmes is able to ...