The Woods by Harlan Coben

Twenty years ago, four teenagers disappeared in the woods. Now, two decades later, everything is changing...
Paul Copeland's sister went missing 20 years ago. Now raising a daughter alone, Cope balances family life with a career as a prosecutor. But when a murder victim is found with evidence linking him to Cope, the well-buried secrets of the past are threatening everything.
Is this body one of the campers who disappeared with his sister? Could his sister be alive...? Confronting his past, Cope must decide what is better left hidden in the dark and what truths can be brought to light...