Abby and Gretchen have been best friends since fourth grade. Through the years, they have bonded over E.T., roller-skating and a shared love for pop music. But when they arrive at high school, things change. Gretchen begins to act…different. As the strange coincidences and bizarre behavior start to pile up, Abby realizes there’s only one possible explanation: Gretchen, her favorite person in the world, has a demon living inside her. And Abby is not about to let anyone or anything come between her and her best friend. With help from some unlikely allies, Abby embarks on a quest to save Gretchen. But is their friendship powerful enough to beat the devil?