Christie wrote a few with that plot twist; sometimes they’re satisfying and sometimes they’re not. I haven’t read Ordeal By Innocence since high school, but do recall that it fell into the “not” category for me.

Yeah, nothing dates quite as badly as psychological explanations for stuff. There are a couple of passages in Ray Bradbury stories that I think were even meant, at the time of writing, to be parodies of such things (the characters pitching them invariably turn out to be wrong)—and they’re *still* breathtakingly annoying to read.