Dead Man's Folly (1956)

Not a classic but a very solid Poirot mystery. I picked it up a) because I hadn't read it before and b) because it featured Ariadne Oliver, probably my favorite recurring Christie character, the dry and self-deprecating mystery novelist. Poirot attends a fete in which there is a scheduled murder hunt, a kind of figure-it-out-yourself mystery devised by Mrs. Oliver. Naturally the young girl who is hired to play the murder victim winds up strangled for real. The solution is both ingenious and a little bit out of left field.