Maura Isles deals with death. As a pathologist in downtown Boston, she has seen more than her share of corpses. But never before has the body on the medical examiner's table been her own. There can be no denying the evidence though. The dead woman is her mirror image right down to the most intimate physical details. Even more chilling is the discovery that they share the same birth date and blood type. Then a DNA test confirms that Maura's mysterious double is indeed her twin sister, and suddenly an already bizarre murder investigation becomes a disturbing journey into a past full of dark and deadly secrets.