The Valley of Fear by Arthur Conan Doyle is the fourth and final Sherlock Holmes novel by British writer Arthur Conan Doyle. It is loosely based on the Molly Maguires and Pinkerton agent James McParland. The story was first published in the Strand Magazine between September 1914 and May 1915. The first book edition was copyrighted in 1914, and it was first published by George H. Doran Company in New York on 27 February 1915, and illustrated by Arthur I. Keller.
Sherlock Holmes receives a cipher message from Fred Porlock, a pseudonymous agent of Professor Moriarty. Holmes deciphers the message as a warning of a nefarious plot against one Douglas, a country gentleman residing at Birlstone House. Some minutes later, Inspector MacDonald arrives at 221B Baker Street with news that Douglas was murdered the night before. The three men travel to Birlstone House to investigate.
Holmes studies the window sill as MacDonald, White Mason, and Watson observe (Strand, 1914).
After interviewing Cecil Barker, a frequent guest at Birlstone House and the man who discovered the body, they agree that suicide is out of the question, and that someone from outside the house committed the murder. Barker explains that Douglas married after arriving in England five years earlier. Barker believes a secret society of men pursued Douglas, and that he retreated to rural England out of fear for his life. Mrs. Douglas said her husband mentioned something called "The Valley of Fear". Holmes learns that the housekeeper heard a sound, as if of a door slamming, half an hour before the alarm; Holmes believes that this sound was the fatal shot.
Local detective White Mason and Inspector MacDonald track a bicycle found on the grounds of the house to an American staying at a guest house. The American appears to be the murderer, but there is no sign of him. Holmes asks MacDonald to write to Barker, telling him that the police intend to search the moat the next day. That night, they lie in wait outside Birlstone Manor and see Barker fish the clothes of the missing American out of the moat. Barker refuses to explain the situation. At that moment, Douglas appears, alive and well. He hands Watson a written account called "The Valley of Fear", which explains why he feared for his life.