A couple of years ago, I found an interesting book at a thrift store: The Final Adventures of Sherlock Holmes. It is a collection of stories, essays, etc, related to Sherlock Holmes, and almost all of them are entirely written by Sir Arthur Conan Doyle. I skimmed through the book; some of the stories I had read before, but others were quite new to me. My favourite was "The Mystery of Uncle Jeremy's Household", which I certainly hadn't ever heard of before.
This story, though not strictly a Holmes story, has a few things in common with the Holmes series. Firstly, it is a mystery; secondly, it has two characters who are much like Holmes and Watson. Hugh Lawrence is the "Watson" character, and John Thurston is the "Holmes" character. Interestingly enough, it's Lawrence who does the detective work. Thurston has a similar personality to Sherlock Holmes's, but he is more interested in his chemical experiments than in solving a mystery. Still, even in the context of a short story, he was such a great character and so like Holmes, that I wish there were more books about him.
The mystery is a classic example of a Sir Arthur Conan Doyle short story--he establishes a great setting, builds up suspense, and brings the reader right into the story through the first-person narration. And while the mystery itself may not be as complex as some of the Sherlock Holmes mysteries, it still keeps the reader interested in "what happens next". If you've read the Holmes series and want to read more, you might want to give this one a try.