A nurse named Katie struggles to save a patient in her care despite a desperate attempt at CPR. Time passes, and she adopts a new identity as Maud, becoming a devoted Roman Catholic. Now working as a private palliative care nurse in a quaint seaside town in England, she is assigned to care for Amanda (Jennifer Ehle), a former dancer and choreographer from the U.S. who is facing stage four lymphoma. Amanda is embittered by her diagnosis and candidly expresses her profound fear of the oblivion that death brings.
In a twist of fate, Maud believes that she has been chosen by God to save Amanda's soul, who has long rejected faith. Their relationship grows as Maud shares her belief in divine presence, and together they experience moments of ecstatic prayer. However, tensions rise when Maud grows wary of Amanda's companion, Carol (Lily Frazer), who regularly visits and has a financial arrangement with Amanda for intimacy.
Determined to protect Amanda’s soul, Maud begs Carol to cease her visits, fearing for her patient’s spiritual wellbeing. Yet, during Amanda's birthday celebration, Amanda publicly derides Maud, revealing that she tried to separate them. In a fit of anger, Maud strikes Amanda, leading to her dismissal from her caregiving position.
Feeling abandoned by God, Maud seeks solace in a local pub but finds herself ostracized. After an encounter that turns traumatic, she is haunted by memories of past failures, including the death of her patient. Her emotional turmoil deepens when she comes across Amanda’s new nurse and sees their amiable relationship, which infuriates her.
In the solitude of her rundown apartment, Maud begs for divine guidance, and feels that God is urging her to prepare for a significant act of faith. She interprets a swirling cloud formation as a holy sign. That night, adorned in a makeshift robe and clutching rosary beads, she sneaks into Amanda's home after the new care nurse has left. There, she finds the frail Amanda in bed, who, seeking forgiveness for her earlier mockery, suggests they reminisce about their shared experience of divine presence—only to reveal that it was all a deception, and that God is just an illusion.
In horror, Maud realizes the truth and a furious confrontation ensues, culminating in her stabbing Amanda in a delirious frenzy, believing she is acting on God's will. The next morning, in a chilling act of despair, Maud walks onto the beach, drenches herself in acetone, and prays, uttering her final words in Welsh—"Glory to God"—before igniting herself in flames. In her last agonizing moments, she envisions angelic wings as onlookers kneel in awe, yet the reality of her pain remains brutally poignant as she screams, trapped in the balance between grace and horror.
