Really you’ve got to expect it. I didn’t know Mark Twain had written detective fiction. Of course he did. Of course he satirizes Sherlock Holmes! Of course the story is set it in a mining camp out West, there being precedent in Conan Doyle’s A Study in Scarlet, published fifteen years before. And of course Twain called his A Double-barreled Detective Story.
The double-barreled is metaphor for two detectives working on the same murder case. Sherlock Holmes uses observation and scientific analysis. Archie Stillman (non de plume) uses his nose for scent analysis. Each detective has strengths and weaknesses — Sherlock Holmes’ weakness is Mark Twain — who burlesqued him mercilessly. (Almost)