Maud, a deeply religious young woman, works as a nurse in a quiet English seaside town. Haunted by a traumatic incident from her past, she has recently converted to Roman Catholicism and is fervently devoted to her newfound faith. Her latest assignment is to provide palliative care for Amanda, a former dancer and choreographer who is terminally ill with cancer. Amanda is worldly and unrepentant in her lifestyle, which Maud perceives as sinful. Maud is initially distressed by Amanda's behavior but becomes convinced that she has been sent on a divine mission to save Amanda’s soul before it’s too late. Maud zealously immerses herself in her mission, seeking signs from God and believing she can feel His presence guiding her actions.

As Maud becomes more obsessed with her purpose, she wrestles with the sharp contrast between her devout faith and Amanda's defiance of it. Her interactions with Amanda grow more intense and alarming as she entangles spiritual fervor with a personal mission for redemption. Drowning in her piety, Maud becomes entrapped in a downward spiral where the boundaries between reality and her religious visions blur, casting doubts on the validity of her mission. The tension heightens as Maud's perception of divine duty and moral obligation drives her further into isolation and a psychological battle with unseen forces. As she battles these internal conflicts, the dissonance within her grows threatening and explosive, endangering herself and those around her.