The Likeness — Tana French

Six months after a particularly nasty case, Detective Cassie Maddox has transferred out of Dublin's Murder squad and has no plans to go back. That is, until an urgent telephone call summons her to a grisly crime scene.

It's only when she sees the body that Cassie understands the hurry. The victim, a young woman, is Cassie's double and carries ID identifying herself as Alexandra Madison, an alias Cassie once used on an undercover job. Suddenly, Cassie must discover not only who killed this girl but, more importantly, who is this girl? And as reality and fantasy become desperately tangled, Cassie moves dangerously close to losing herself forever.