Dr. Martha Livingstone is a psychiatrist tasked with assessing the mental state of a young novice nun following a tragic death at a convent. As a secular professional with a distrust of organized religion, she approaches the case with a determination to uncover the scientific and psychological facts. Her interactions with the convent are colored by her own history with Catholicism, the loss of her sibling, and her personal struggles with the concept of motherhood.

Agnes is a young, sheltered novice nun at a convent who is under investigation following the discovery of a dead infant in her room. She possesses an ethereal singing voice and a highly literal, childlike understanding of faith. Having been raised in severe isolation, she struggles to comprehend the world outside the convent and insists she has no memory of giving birth, attributing her experiences to angels and divine intervention.

Mother Miriam Ruth is the Mother Superior of the convent and acts as a guardian for the younger nuns. Having experienced marriage and motherhood before taking her vows, she possesses an empathetic understanding of the secular world that contrasts with her current cloistered life. She acts as a formidable shield between her convent and the investigating psychiatrist, preferring to view the events through the lens of faith and spiritual possibility rather than psychological pathology.

Marie is Dr. Livingstone's younger sister who chose to enter a convent at the age of 15. Her time in the convent and subsequent medical neglect severely impacted her family, permanently altering her older sister's view of religious authority and institutions.

Father Marshall is a shy priest who visits the convent to perform religious duties. He serves as one of the few male figures in the nuns' highly insulated environment, interacting with them primarily through the confessional.

Agnes's late mother is a formative figure in the young nun's life, having raised her in extreme isolation. Her rigid, frightening approach to parenting and religion left a profound psychological imprint on her daughter's understanding of the physical world.

Maurice is a Frenchman and Dr. Livingstone's former fiancé. Their relationship highlights the differing views on parenthood and family that shape the psychiatrist's current perspectives on motherhood and independence.

Sister Margaret is a nun at the convent. She assists in managing the immediate aftermath of the tragic discovery, serving as a procedural link between the religious community and secular law enforcement.

Sister Paul is a nun whose death coincides with the timeline of Agnes's mysterious pregnancy. Her passing marks a significant night in the convent's recent history.