There’s Someone Inside Your House by Stephanie Perkins
Makani Young thought she’d left her dark past behind her in Hawaii, settling in with her grandmother in landlocked Nebraska. She’s found new friends and has even started to fall for mysterious outsider Ollie Larsson. But her past isn’t far behind.
Then, one by one, the students of Osborne Hugh begin to die in a series of gruesome murders, each with increasingly grotesque flair. As the terror grows closer and her feelings for Ollie intensify, Makani is forced to confront her own dark secrets.