The Valley of Fear was published by Arthur Conan Doyle in serial form in the Strand Magazine between September 1914 and May 1915 in Great Britain before appearing in book form in the US later in 1915. 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 a fully fleshed out novel-length engagement with the most famous resident of Baker Street. The term “fleshed out novel-length engagement” is far more appropriate than, say, “Sherlock Holmes novel” since it shares with A Study in Scarlet and The Sign of Four one of less popular aspects of the entire Holmes canon: a Sherlock-less explanatory section in flashback that goes longer than it probably needs, although on its on merit it is indeed a fascinating read. A fascinating read, but relevant for enjoying what might have been a quick-moving and very captivating short story that is a bit longer than most. Not only is the flashback explanation going to prove needlessly prolonged for certain readers, for every reader it takes up more words than the opening section that is actually a pretty dazzling example of just how inventive a writer Conan Doyle could be when his hear was really in it.
Another element that the later novel shares with A Study in Scarlet is that the flashback section inserted after Holmes has put his deductive power to work solving the mystery situates 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 your 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 guerilla warriors in the battle for fair and honest treatment of coal miners by a ownership class not above engaging Pinkerton Detective to dispense their equally violent agenda for keeping the unions under control.
How much one enjoys The Valley of Fear is likely turn on 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 which flesh things out with the utterly Holmes-less flashback sections. At least that novel fills time with Watson’s interaction with other characters, however. Doyle set to work constructing The Valley of Fear in a very deliberate fashion in the two parts and an additional coda are literary conventions subtly employed by the author as a means of manipulating the story’s very palpable tension.
On the other hand, readers who enjoy the addition of a historical context to their fiction as a means of expanding their understanding of the central narrative should find The Valley of Fear to be one of the more rewarding surprises in their journey throughout the entirety of the Sherlock canon. The biggest mystery here may be, in fact, just why The Valley of Fear is less well known, anthologized and filmed than the rather shockingly Sherlock Lite experience that is The Hound of the Baskervilles. Ultimately, once the flashback explanatory section is put into context and The Valley of Fear is approached more on the terms it seems Doyle was going for rather than as merely another episode in Holmes catalogue, it should start to become clear that what you have just finished is more akin to an Edwardian psychological thriller than a Sherlock Holmes detective story.