The 21st century is a good time to be Sherlock Holmes. He stars in the Guy Ritchie films, with Robert Downey, Jr.; an internationally popular BBC television series featuring Benedict Cumberbatch; a novel sanctioned by the Arthur Conan Doyle Estate; and dozens of additional novels and short stories, including two by Neil Gaiman. Add to this the videogames, comic books, and fan-created works, plus a potent Internet and social media presence. Holmes'...