This book was so damn charming. It's a fun but scary read about two friends (best friends) who grew up together. They met awkwardly at a birthday party for Abby, where Gretchen was the only attendee. Abby was more worldly, came from the wrong-side-of-the-tracks, etc. Gretchen grew up in a white collar family, sheltered from anything that could possibly harm her.
The book jumps ahead to Gretchen and Abby in High School. One night, while out at a friend's lake house, they and a couple other girls, decide to try LSD. Gretchen strips off her clothes and disappears into the woods. When Abby finds her, she's disheveled and visibly shaken.
The friends head back home and Gretchen changes, dramatically.
The novel takes place in the 80's in a private, Christian school. There's a lot of nostalgia in this book which makes it fun, the whole demonic possession makes it scary, and the relationship between the Gretchen and Abby makes it touching.