Third Girl by Agatha Christie

A troubled young woman named Norma approaches Poirot, claiming she might have committed a murder—but then disappears. As Poirot and his friend Ariadne Oliver search for answers, they uncover a web of manipulation involving her two flatmates, a missing father, and a hidden past. The investigation leads to a shocking truth buried beneath Norma’s fragmented memories. The story explores psychological themes and the fragility of identity. It’s a haunting mystery with a deeply personal core.