Mary is a young secretary who grew up in an impoverished Pennsylvania orphanage. Eager to build a professional life and leave her difficult past behind, she secures a coveted position working at the Nettleton State Village. She is observant and diligent, but her longing for security and a maternal figure occasionally clouds her judgment regarding the institution's true nature.

Dr. Vogel is the wealthy, elegant founder and superintendent of Nettleton State Village for Feebleminded Women of Childbearing Age. As a prominent eugenicist and early female psychiatrist, she advocates for women's rights while simultaneously policing the bodies of those she deems socially unfit. She uses her aristocratic charm and political connections to mask her rigid class prejudices and illicit operations.

Lillian is a highly intelligent, courageous young woman who grew up alongside Mary at St. Catherine's Orphan Asylum. Despite her fluency in multiple languages and musical talents, she is incarcerated at Nettleton due to her defiance of social and racial norms. Her presence at the institution contradicts the official narrative regarding the inmates.

Jake is a Jewish journalist from New York reporting on local labor disputes and institutional corruption. He is highly educated, observant, and driven by a strong moral compass shaped by his personal experiences with discrimination. His dedication to exposing systemic abuses places him at odds with the region's elite.

Roberta, known as Bertie, is a young, widowed nurse employed at Nettleton. Sociable and well-liked in town, she provides medical care at the facility but increasingly questions the ethical implications of how the inmates are treated. She serves as an early confidant and guide for Mary.

Charlie is Dr. Vogel’s designated driver. Though initially presenting a gruff exterior, he possesses deep ties to the local working-class community and understands the harsh realities of the institution better than he lets on.

Miss Hartley is the assistant superintendent at Nettleton State Village. She works closely with Dr. Vogel to manage the daily operations of the facility and enforces strict discipline among the inmates and lower-level staff.

Hal is a friendly young man who, along with his wife Betty, provides lodging for Mary when she first arrives at Nettleton. He represents the ordinary, working-class staff employed by the institution.

Betty is Hal's affable wife who shares her home with Mary. She is busy raising her young children on the Nettleton grounds and maintains a friendly relationship with the institution's dairy workers.

Gladys is Mary's initial roommate and a fellow secretary at Nettleton. She comes from a working-class background and finds herself displaced and resentful when Mary receives a sudden promotion over her.

Teddy is Mary’s deceased uncle and a former police officer who frequently visited her at the orphanage. His abusive actions during Mary's childhood cast a long shadow over her adult life and psychological development.

Mary's father is an absent parent with a criminal background who worked as hired muscle to brutalize striking union workers. He abandoned Mary at the orphanage following her mother's death.

Graham is a talented Black jazz musician who tours internationally. His relationship with Lillian places him in severe, life-threatening danger due to the racially segregated laws and violent prejudices of the era.

Tom is a vulgar local speakeasy owner who converted his father's blacksmith shop into an illicit bar. He uses the prejudiced legal system to punish those who defy his control.

Mr. Whitcomb is a wealthy and influential bank president. He leverages his elevated social standing to abuse the vulnerable young women hired out to work in his home as maids, avoiding legal repercussions through bribery.

Ida is an inmate at Nettleton described as having the reasoning skills of a toddler. Rented out as a maid to a local wealthy family, she becomes a victim of severe exploitation and assault.

Cloris is an attendant who manages the dairy farm operations at Nettleton, overseeing inmates assigned to heavy labor. Though she presents a gruff exterior, she harbors a practical understanding of the facility's injustices.

Sister Rosemary is a nun at St. Catherine's Orphan Asylum who helped raise Mary and Lillian. She provides the girls with moral instruction and relies on farm-based metaphors to teach them about the dangers of predatory men.

Judge Filmore is a corrupt local magistrate who routinely sentences marginalized women to Nettleton. He actively assists Dr. Vogel in managing an illicit bootlegging operation under the guise of institutional governance.

Mother Beatrice runs the St. Catherine's Orphan Asylum where Mary and Lillian spent their childhoods. She serves as a distant authority figure who Mary contacts when attempting to secure religious services for the Nettleton inmates.

Brooks is a philosophy professor at a local university. He embodies the casual sexism of the era, struggling to comprehend a woman holding a position of supreme medical authority.

Elsie is a non-verbal inmate at Nettleton who possesses extraordinary musical talent. Her advanced abilities on the piano sharply contradict the institution's claims regarding the intellectual capacities of the women housed there.

Olga is the cruel matron of Building Five, the severe punishment block at Nettleton. She exhibits intense malice toward the inmates placed under her control, subjecting them to degrading and unsanitary conditions.

Ike is a journalist and colleague of Jake Enright. He utilizes documented evidence to expose the systemic corruption and hazardous working conditions at the state village to the public.