What starts out as a typical golden-age mystery (with diagrams and maps) ends as a cat-and-mouse romp. We're told whodunnit a third of the way through, then the rest concerns how the Inspector (and a number of friends) plot to thwart the criminal who is so clever that he cannot be brought to trial for his crimes. (The murderer is so clever that he makes Dr. Moriarity look like a bumbling fool.) I found the last part tiresome (including 19 pages detailing a car chase through the countryside) and wound up skimming a lot at the end.
