My Best Friend's Exorcism - Grady Hendrix

From the New York Times best-selling author of The Southern Book Club's Guide to Slaying
Vampires, this unholy hybrid of Beaches and The Exorcist blends teen angst and unspeakable horrors into a pulse-pounding supernatural thriller.

The year is 1988. High school sophomores Abby and Gretchen have been best friends since fourth grade. But after an evening of skinny-dipping goes disastrously wrong, Gretchen begins to act…different. She’s moody. She’s irritable. And bizarre incidents keep happening whenever she’s nearby. Abby’s investigation leads her to some startling discoveries—and by the time their story reaches its terrifying conclusion, the fate of Abby and Gretchen will be determined by a single question: Is their friendship powerful enough to beat the devil?