Arthur Conan Doyle published The Valley of Fear in serial form in Strand Magazine between September 1914 and May 1915. A book form followed the British serialization in 1915. The manuscript, 176 folio pages with Doyle’s deletions and revisions, shows that Watson was not intended to be the original narrator. It is the only Holmes tale to deal directly with Irish issues.
Like A Study in Scarlet, one of the more famous Holmes tales, The Valley of Fear features a flashback section inserted after Holmes has put his deductive power to work solving the mystery. This places the reader across the Atlantic Ocean and firmly on the solid ground of actual American history. The historical impetus behind the plot of The Valley of Fear was the real confrontation between the Pinkerton Detective Agency and members of an Irish secret society known as the Molly Maguires who had emigrated to Pennsylvania. Depending on one’s point of view, the Molly Maguires were either just a collection of mindlessly violent vigilantes who just so happened to have targeted the anti-union owners of coal mines, or they were guerrilla warriors in the battle for fair and honest treatment of coal miners by an ownership class that wasn't above engaging Pinkerton Detective to dispense their equally violent tactics for keeping the unions under control.
Conan Doyle had visited America on a lecture tour to great acclaim in the 1890s and returned to New York City in May of 1914. It is likely he discussed The Valley of Fear with his American editor. It is also likely that his editor recommended that the American publication elide three words from the second part of the tale: “coal and iron” from the sentence “Captain Marvin is my name—of the Coal and Iron Police.” A more neutral word, “mine,” was substituted (264).
Like The Sign of Four, The Hound of the Baskervilles, and the origin of Sherlock Holmes (A Study in Scarlet), The Valley of Fear is no mere short story, but rather a fully fleshed out, novel-length engagement with the most famous resident of Baker Street. This description of the work is far more appropriate than, say, “Sherlock Holmes novel,” since the work shares with A Study in Scarlet and The Sign of Four one of the less popular aspects of the entire Holmes canon: that explanatory section in flashback. This arguably goes on longer than it probably needs to, although, to its merit, it is indeed a fascinating read. It may feel needlessly prolonged for certain readers (it consists of more words than the opening section) but it is actually a pretty dazzling example of just how inventive a writer Conan Doyle could be when his heart was really in it.
How much one enjoys The Valley of Fear likely depends whether one enjoys the other three novels featuring Sherlock more than one enjoys the many short stories. Even what is arguably the most famous Holmes mystery of them all—The Hound of the Baskervilles—is as light on actual Sherlock-centric scenes as the novels that have many Holmes-less flashback sections (Hound fills time with Watson’s interaction with other characters, however). Doyle set to work constructing The Valley of Fear in a very deliberate fashion, with two parts and an additional coda; these are literary conventions subtly employed by the author as a means of manipulating the story’s very palpable tension. Readers who enjoy historical context to their fiction as a means of expanding their understanding of the central narrative should find The Valley of Fear one of the more rewarding surprises in their journey throughout the Sherlock Holmes canon.
The biggest mystery here may be, in fact, just why The Valley of Fear is less recognized, anthologized, and filmed than The Hound of the Baskervilles. Ultimately, once the flashback explanatory section is put into context and The Valley of Fear is approached more on Conan Doyle's intended terms rather than as merely another episode in the Holmes catalogue, it should start to become clear that the novel is more akin to an Edwardian psychological thriller than to a Sherlock Holmes detective story.