Nobody's Fool by Harlan Coben

PI Sami Kierce is teaching a night school class when a woman walks in. Sami believes she is Anna, a girlfriend he last saw over twenty years ago. In fact, back then, Anna was last seen covered in blood and presumed dead--with Sami next to her in bed. Sure that the woman is Anna, Sami tries to follow her to figure out what's going on, but Sami's investigation ends up raising way more questions than answers. In Nobody's Fool, Coben writes another multi-layered puzzle of a novel that's hard to put down.