An outstanding series of mystery-deduction stories. The hero is Professor S.F.X Van Deusen, aka "The Thinking Machine". I first read a book of some of those stories when I was young, and they made a pretty big impression on me. They're extremely clever and unique.Futrelle himself was an interesting character, not least in the manner of his death: he was on the maiden voyage of the Titanic. With him, when he died, were several manuscripts for Thinking Machine stories - now lost forever, of course.Jacques Futrelle's official site contains the full text of fifty Thinking Machine stories. I recommend starting with "The Problem of Cell 13". Yes, they're old, but they're really good.