The Valley of Fear is the fourth and final Sherlock Holmes novel by Sir Arthur Conan Doyle.

Sherlock Holmes receives a cipher, without the key. He is able to deduce that it is a book cipher and after a few failed attempts, he finally deciphers the message. Holmes is able to decipher the message as a warning, and with the help of Watson, attempts to solve a crime.

Sir Arthur Conan the British writer, who created the character Sherlock Holmes was originally a physician himself. He published four novels and more than fifty short stories about Holmes and Dr. Watson. The Sherlock Holmes stories are generally considered milestones in the field of crime fiction.

The character and stories have had a profound and lasting effect on mystery writing and popular culture as a whole, with the original tales as well as thousands written by authors other than Conan Doyle being adapted into stage and radio plays, television, films, video games, and other media for over one hundred years.