The Secret Sister by M. M. DeLuca

Anna is on a mission to find out how and why her sister Birdie disappeared. Will she ever be able to uncover the truth? This addictive thriller will keep you guessing until the last twist.

Anna and her sister Birdie grew up in foster care, moving from home to home, often abused and neglected, until finally Anna lost track of Birdie. Years later, Anna is working as a teacher and married to Guy, a loving man from a wealthy family. Anna wants to tell Guy about her past and about Birdie, but before she can do that, she needs to find out what happened to her sister.

Perfect for fans of The Perfect Couple, Lisa Jewell, and Phoebe Morgan.