Girl, Forgotten - Karin Slaughter

Prom Night, Longbill Beach, 1982. Emily Vaughn dresses carefully for what's supposed to be the highlight of any high school career. But Emily has a secret. And by the end of the night, because of that secret, she will be dead.

Nearly forty years later, Andrea Oliver, newly qualified as a US Marshal, receives her first assignment: to go to Longbill Beach to protect a judge receiving death threats. But Andrea's real focus isn't the judge - it's Emily Vaughn. Ever since she first heard Emily's name a year ago, she's been haunted by her brutal death. Nobody was ever convicted - her friends closed ranks, her family shut themselves off in their grief, the town moved on - so the killer is still out there. But now Andrea has a chance to find out what really happened...