Writing at the Wall Street Journal, Sarah Weinman has written an excellent appreciation of Margery Allingham, one of Britain's "Crime Queens" of the Golden Age and beyond, whose detective, Albert Campion, matured nicely over the course of the books, from a rather foppish young man to a much sharper and better investigator. Allingham's books are always hard to classify - some were classic mysteries, others were thrillers and the best were amalgams of several genres. If you don't know Campion and Allingham, this article will give you a good reason to become acquainted with them; if you do know them already, you'll enjoy the article even more.
One warning - unless you're a subscriber to the Journal online, the link to the (free) article will disappear after this Thursday - so read it now, while you still can. It's worth your time.