In small-town Montana during the early 1990s, a teenage girl, Cameron Post, grapples with her sexual identity amidst the conservative surroundings. Her situation is brought to a head when she is caught in a moment of intimacy with her best friend Coley at a school dance. This discovery is met with swift and decisive action from her Aunt Ruth, who is her guardian after the death of her parents years earlier. Viewing Cameron's sexuality as a sinful deviation that needs correction, Aunt Ruth enrolls her in God's Promise, a remote gay conversion therapy center designed to re-educate its residents about their sexual orientation.

At God's Promise, Cameron encounters a group of youths undergoing similar treatments. The establishment is run by Dr. Lydia Marsh and her brother, Reverend Rick, a supposed example of a successful conversion. As Cameron navigates the center's programming, which includes psychologically invasive therapy sessions and moral instruction, she begins to form strong bonds with fellow "disciples" Jane and Adam. These friendships become her solace and a source of support as they each deal with their own conflicted feelings about their identities and the center's methods. The pressures and expectations within God's Promise prompt Cameron to confront the nature of her desires and the painful realization that authenticity comes at a personal cost within an intolerant society.