Baldacci, David. Atlee Pine series

Sequel to: Daylight

As the long search for twin sister Mercy reaches its conclusion, FBI agent Atlee Pine, when the truth is finally revealed, will face the greatest danger yet, one that could cost her everything

For her entire life FBI Agent Atlee Pine has been searching for her twin sister, Mercy, who was abducted at the age of six. Shortly after, Atlee's parents inexplicable abandoned her. Now Atlee has discovered the reason for their abandonment-- and proof that Mercy survived her abduction and escaped. Atlee has no idea if her sister is still alive... but the final leg of her search may well cost Atlee everything. -- adapted from jacket