After her parents die in a car accident, Cameron Post is left in the care of her grandmother and devout Aunt Ruth. Soon, Colie Taylor appears in their town, and Cameron spends all her time with her. However, Cameron quickly realizes that her feelings for Colie are more than just friendship. Upon learning of their forbidden relationship, Aunt Ruth sends her niece to a religious school, where Cameron will not only find new friends, but also learn a lot about herself and the world.

A feature film of the same name, starring Chloë Grace Moretz, was made based on the book, winning the top prize at the 2018 Sundance Film Festival.