The Return of Sherlock Holmes
Various in each story
We actually get a new antagonist each story, since we are dealing with thirteen separate stories here. Aside from the deceased Professor Moriarty, who we hear about mainly in the "Empty House," Holmes doesn't really have a recurring antagonistic rival. Instead, we get a new villain, or villains, each story. These villains are also quite different from each other: we have women and men, Britons and foreigners, young and old people. The antagonists here commit crimes for a variety of reasons too: desperation, self-defense, by accident, or by careful planning. The crimes themselves are as varied as the people who commit them as well. Perhaps the one common element among these antagonists is that there really isn't one; all kinds of people can commit crimes. Importantly, not every criminal is "evil" in these stories, and not every bad, rude, or obnoxious person is an actual criminal here. A good example is the Duke in the "Priory School," who is a bad father and a sometimes opponent to Holmes, but not an actual criminal.