Pretty girls by Karin Slaughter

Twenty years ago Claire Scott's eldest sister, Julia, went missing. No one knew where she went - no note, no body. It was a mystery that was never solved and it tore her family apart.

Now another girl has disappeared, with chilling echoes of the past. And it seems that she might not be the only one.

Claire is convinced Julia's disappearance is linked.

But when she begins to learn the truth about her sister, she is confronted with a shocking discovery, and nothing will ever be the same...