Vicious Little Darlings — Katherine Easer

Sarah Weaver wasn't looking forward to starting at an all-girls school. But that was before she met Maddy. Maddy and her best friend, Agnes, are fun and rich and interesting-and for some reason, they seem to really like Sarah. Before long, Maddy and Agnes have moved Sarah into a big house off campus, where they cook together, buy each other presents, and share each other's secrets. So why does Sarah feel like something's bizarrely wrong? As more and more cracks start to show in Maddy's and Agnes's perfect veneers, Sarah notices some strange and disturbing things: Maddy's compulsive lying, Agnes's obsession with Maddy, and the deterioration of their friendship. And just when Sarah begins to question her own sanity, things turns deadly.