Unspeakable Things by Jess Lourey

Inspired by a terrifying true story from the author's hometown, a heart-pounding novel of suspense about a small Minnesota community where nothing is as quiet—or as safe—as it seems.
Cassie McDowell's life in 1980s Minnesota seems perfectly wholesome. She lives on a farm, loves school, and has a crush on the nicest boy in class. Yes, there are her parents' strange parties and their parade of deviant guests, but she's grown accustomed to them.
All that changes when someone comes hunting in Lilydale.
One by one, local boys go missing. One by one, they return changed—violent, moody, and withdrawn. What happened to them becomes the stuff of shocking rumors. The accusations of who's responsible grow just as wild, and dangerous town secrets start to surface. Then Cassie's own sister undergoes the dark change. If she is to survive, Cassie must find her way in an adult world where every sin is justified, and only the truth is unforgivable.