For her entire life, FBI agent Atlee Pine has been searching for her twin sister, Mercy, who was abducted at the age of six and never seen again. Mercy's disappearance left behind a damaged family that later shattered beyond repair when Atlee's parents inexplicably abandoned her. Now, after a perilous investigation that nearly proved fatal, Atlee has finally discovered not only the reason behind her parents' abandonment and Mercy's kidnapping, but also the most promising breakthrough yet: proof that Mercy survived her abduction and then escaped her captors many years ago.