Hallowe'en Party by Agatha Christie

Agatha Christie wrote this mystery late in her career, and there are definite moments of nostalgia, but it's also well-plotted and quite engaging. As Poirot explains just what was going on (which, on reflection was all there in the earlier parts of the story) to his friend Ariadne Oliver, there's lots of allusion: we get our own Lady MacBeth! I was very satisfied with this mystery.