The Return of Sherlock Holmes is where Doyle and Holmes really hit their stride. It’s not really till this book (after three novels and two volumes of short stories) that Holmes becomes the prickly eccentric asshole we all know and love. Prior to this, he is a run-of-the-mill genius with fairly average social skills. In The Return, Holmes becomes positively erratic and Watson finally acknowledges how challenging he can be.
The biggest thing, though, is the stories. The Solitary Cyclist isn’t one of Doyle’s best known, but it remains one of the most suspenseful tales I’ve ever read. Revisiting it as an adult (female solitary cyclist), I’m even more struck by how well he captured the terrible anxiety of being a lone woman followed by a man on an empty stretch of road. Awesomely, Doyle doesn’t make her a victim. She is, in fact, a real badass, especially given her time and not just because she rides a bike.
Better known stories that I also adore include The Empty House, The Norwood Builder, Charles Augustus Milverton, and The Second Stain.