In a time when demonic possessions are on the rise, the Catholic Church reopens exorcism schools to train priests in the rite of exorcism. Sister Ann, a young and compassionate nun with a tumultuous past, is deeply affected by the plight of those possessed, but her gender bars her from performing exorcisms which are traditionally carried out by priests. Despite this prohibition, Ann harbors a profound belief that she has a calling to battle evil entities. When she encounters a young girl named Natalie, who is exhibiting alarming signs of demonic possession, Sister Ann becomes increasingly convinced that she must help the tormented child.

As Natalie's situation grows more dire, Sister Ann seeks guidance from Father Quinn, a professor of the exorcism class at her school. Father Quinn recognizes Ann's deep faith and her potential in the fight against demonic forces, bending the rules to tutor her in the art of exorcism. Through her unorthodox training, Ann is thrust into a male-dominated realm where she confronts not only the skepticism of the Church's authorities but also her own inner demons. As she delves deeper into the dark world of exorcisms, Sister Ann becomes embroiled in a spiritual battle that challenges the boundaries of her faith and forces her to face the complex interplay between good and evil.