3 girls and a teacher from an Australian private academy disappear after climbing up to the titular Hanging Rock during their school picnic.  No bodies are ever found, and the event haunts everyone remotely connected to it, some more tragically than others. There's a hint of something supernatural about the whole thing, but it's never confirmed. While the truth of the mystery was published decades later, I don't thinks it's needed. It'd less about the mystery and more about how their absence affects their world. A little slow, but really interesting, and weird enough to be right up my alley.