The Bone Forest by Sarah Cooley

Sixteen-year-old Alessa Hale is seeking answers in the disappearance of her older sister, Aria, who wandered into the forest near their home in Pine Hollow, South Dakota, and never returned. Two months later, Aria stumbles into town, soaked in blood, with no memory of her disappearance, striking fear in the locals and causing turmoil within Alessa’s family. Her parents, already strained by grief and loss, try to hide Aria’s violent behavior and bizarre outbursts from the prying eyes of their neighbors to keep up appearances. When several more townsfolk vanish into the woods with no explanation, the police immediately suspect Aria. But Alessa's parents seem more concerned with maintaining their public image as good Catholics than supporting Aria through the detectives' dogged investigation. Soon, Alessa will question the motives of everyone around her, including the town’s priest, Father Samuel, who believes Aria is beyond help. In the midst of all the chaos, Aria’s behavior becomes increasingly unpredictable. She refuses to eat, she barely speaks, and she claims to hear voices calling to her from deep inside the fores t. Police amp up their investigation upon hearing rumors spread by frightened citizens who have witnessed her erratic behavior. In a desperate attempt to save her sister, Alessa is determined to uncover the truth, and learn how and why this happened to Aria. If she can't uncover the truth, she'll lose her sister and her own life to religious zealots, relentless detectives...or something far, far worse.