Which Sherlock Holmes novel features the criminal group called the Scowrers?

The Valley of Fear features the criminal group called the Scowrers.

Arthur Conan Doyle’s 1915 novel alternates between a present-day Holmes investigation and a historical narrative set in Vermissa Valley, Pennsylvania. The Scowrers are a violent secret society that controls local life through intimidation, extortion, and murder.

The novel’s second section is strongly associated with the real-life Molly Maguires, a nineteenth-century miners’ organization in Pennsylvania. Doyle transformed historical inspiration into fictional characters and events, including the Pinkerton detective Birdy Edwards.

The title refers both to the threatening atmosphere surrounding the mining community and to the dangers uncovered by Holmes. Unlike many Holmes adventures, the novel spends substantial time away from Baker Street and gives its historical backstory almost equal importance to the detective plot.