Snow Creek by Gregg Olsen

Footprints were scattered about like fallen leaves. She looked down into the ravine, and once more her lungs filled with fear. A body, blackened and motionless lay splayed out in the bushes.
Detective Megan Carpenter is no stranger to evil. Escaping the horrors of her old life, she's vowed never to let anyone hurt her or those she loves ever again. Joining the small police force in Jefferson County's Port Townsend, Megan is determined to get every victim of a crime the justice they deserve.
So when Ruth Turner walks into the Sheriff's office claiming her sister Ida Watson has been missing for over a month, Megan's instincts tell her that she needs to do more than just file a report.
Arriving at a secluded farmhouse in the hills above Snow Creek, she finds Ida's teenage children alone and frightened. Then a few days later, close to the Watsons' home, the blackened body of a woman is discovered in an abandoned pickup truck.
Megan must unravel the disturbing secrets of the isolated Snow Creek community if she is to catch the killer.
But Megan has dark secrets of her own too.
Hidden in the back of her closet is a box of tapes containing every single recording of her therapy sessions with Doctor Albright over thirteen years ago. As Megan begins to play the tapes, she's taken straight back to her terrifying childhood, back to the time she was a kid called Rylee, fighting to survive.
Can Megan finally confront the past she's spent years trying to block out and will listening to her own painful story help her solve the complex case she is now entangled in?