Devout evangelical Christian Mary Cummings is about to embark on her senior year at American Eagle Christian High School, located near Baltimore. Together with her friends, Hilary Faye and Veronica, they have created a girl group called the Christian Jewels. One day, while enjoying a swim in his pool, Mary's boyfriend, Dean Withers, reveals his suspicion about his own sexuality. Stunned and disoriented, Mary accidentally hits her head, leading to a vision in which Jesus encourages her to help Dean. With the belief that Jesus will forgive her, she decides to lose her virginity to him in an attempt to "straighten" him out.
Unexpectedly, Dean's parents find gay pornography in his room and send him off to a Christian treatment center, Mercy House. The revelation shakes Mary's circle of friends to their core, except for Roland, Hilary's sarcastic paraplegic brother. Soon after, Mary discovers that she is pregnant with Dean's child. As her due date approaches, she chooses to hide her pregnancy from her classmates and her mother, Lillian, who is secretly dating the school's principal, Pastor Skip. Misguided and feeling abandoned by Jesus, Mary grapples with shaken faith as her friends react negatively to Dean's situation. In a fit of rage, Hilary expels Mary from the Jewels, replacing her with unpopular student Tia. The trio – Hilary, Veronica, and Tia – tries to exorcise Mary in a public confrontation, leading to an altercation where Hilary hits her with a Bible.
By Christmas, only Cassandra, a rebellious Jewish student, knows about Mary's pregnancy. As Mary befriends Cassandra, she becomes increasingly isolated from her peers. Meanwhile, Skip's son, Patrick, attempts to get close to Mary, which adds to Hilary's frustrations. In retaliation for Hilary's relentless bullying, Cassandra and Roland expose embarrassing photos of Hilary from her past. The following day, the school becomes a target for vandalism featuring obscene anti-religious messages. Suspicions fall on Mary, Cassandra, and Roland when Skip discovers spray paint cans and a sonogram of Mary's baby in their lockers, planted by Hilary to shift blame.
Unfortunately, Cassandra faces expulsion while Mary and Roland are barred from attending prom. Skip threatens to end his relationship with Lillian unless she enrolls Mary in Mercy House. However, Roland uncovers proof of Hilary's wrongdoing through her credit card statement for the spray paint. Together with Cassandra and Patrick, Mary decides to crash the prom, despite Hilary's attempts to expel them. Roland confronts Hilary with the evidence, and tired of her deceit, Tia corroborates their claims.
In a dramatic turn, a humiliated Hilary bursts outside just as Dean arrives with his boyfriend, Mitch, alongside other residents from Mercy House. Mary seizes the moment to reveal her pregnancy to Dean amidst the chaos. A confrontation ensues with Skip trying to expel the Mercy House residents, but their courage prevails and they stand their ground. Just then, Hilary, in a fit of emotion, recklessly drives through the parking lot, crashing into the school's effigy of Jesus. In a moment of vulnerability, she expresses remorse for her actions and finds comfort from Cassandra. As this turmoil unfolds, Mary unexpectedly goes into labor and must rush to the hospital.
At the hospital, Mary welcomes a baby girl into the world. As Skip arrives with flowers, pondering whether to enter, a nurse captures a photo of the moment. In her voice-over, Mary reflects on her journey, expressing that she has rekindled her belief in a loving God who supports those committed to helping others in need.
