The Valley of Fear
Arthur Conan Doyle
Publisher: Project Gutenberg
Summary
Sherlock Holmes and Dr. Watson receive a letter from an informant who is known by the pseudonym Fred Porlock. Porlock is part of Professor Moriarty's criminal organisation. The letter is written in a numeric code, and Holmes realises that the numbers refer to words in a book , by page and column. They decode the letter (finding the book in question to be Whitaker's Almanack), which warns that John Douglas of Birlstone House is about to be murdered.