The Valley of Fear is a Sherlock Holmes novel by Sir Arthur Conan Doyle. The story was first published in the Strand Magazine between September 1914 and May 1915. The first book edition was published in New York on February 27, 1915.
The Valley of Fear is also notable for the involvement of Professor Moriarty, which contradicts the timeline of the stories. In "The Final Problem", Dr. Watson was first alerted by Sherlock Holmes to the existence of Professor Moriarty. In the same story, Professor Moriarty dies in the confrontation with Sherlock Holmes, as explained in "The Adventure of the Empty House", leaving no time in between the two events for any other story regarding the Professor. However, in The Valley of Fear, Professor Moriarty has been mentioned by Sherlock, and Dr. Watson had appeared to know both about the Professor's evil acts, and the fact that the existence of Moriarty is unknown by nearly everyone except Holmes.
The plot of the novel is based very loosely on the real-life activities of the Molly Maguires and, particularly, of Pinkerton agent James McParland.
The novel is divided into two parts: in the first, Holmes investigates an apparent murder and discovers that the body belongs to another man; and in the second, the story of the man originally thought to have been the victim is told.