Abby and Gretchen have been best friends since fifth grade, when they bonded over a shared love of E.T., roller-skating parties, and scratch-and-sniff stickers. But when they arrive at high school, things change. Gretchen begins to act . . . different. And 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. Gretchen starts randomly bleeding and has strange flashbacks and fits. She refuses to change her clothes, preferring to douse herself with United Colors of Benetton perfume to mask the fact that she hasn't showered in weeks. Then, out of nowhere, she seems to recover. But the oddities simply go from physical to psychological she manipulates their circle of friends so that bad things multiply (including a particularly horrific scene involving a tapeworm), and no one but Abby recognizes what's happening. 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?"