For a three-act plot analysis, put on your screenwriter’s hat. Moviemakers know the formula well: at the end of Act One, the main character is drawn in completely to a conflict. During Act Two, she is farthest away from her goals. At the end of Act Three, the story is resolved.
Here at Shmoop, we usually analyze a novel (or a single short story) in terms of its complication and then resolution. The characters go on some kind of journey, they progress, crisis comes, we all learn an important lesson of some kind, and that's the end of it. But because The Adventures of Sherlock Holmes is a short story collection, we can't really apply that formula. After all, Conan Doyle expressly designed these stories to be self-contained. So there's not much development across stories within the Adventures (though there might be, arguably, across the trajectory of the entire collection of Sherlock Holmes novels and stories). See our detailed summaries for a precise description of the plot; for more analysis, check out our thoughts on "Characters" and "Themes."