Mairin is a fifteen-year-old girl with a rebellious streak and a deep love for reading, music, and the outdoors. Following a frightening incident with her stepfather, her mother places her in the strict Home of the Good Shepherd. She possesses a natural leadership ability and a fierce refusal to be broken by unjust rules, driving her to organize resistance among her peers.

Angela is a blonde teenager sent to the Home of the Good Shepherd by her grandmother due to her attraction to girls. She endures severe abuse under the institution's supposed care, specifically at the hands of the staff physician. She finds solace in books and quiet solidarity with her peers, maintaining her compassion despite her deep emotional wounds.

Colm is Deirdre's second husband and Mairin's stepfather. He spends most of his earnings on alcohol and behaves aggressively toward his family. His abusive actions directly trigger Mairin's removal from her home and placement in the Good Shepherd institution.

Dr. Gilroy serves as the physician for the Home of the Good Shepherd. He uses his position of unchecked authority to prey upon the vulnerable girls under the guise of administering medical treatments.

Helen is a Chinese American teenager residing at the Home of the Good Shepherd while her parents are detained overseas. She copes with her isolation by keeping a detailed journal in Chinese characters to evade the nuns' censorship. Resourceful and observant, she secretly collects laundry tabs to create a makeshift game for the girls to play.

Odessa is a Black teenager sent to the Home by the courts after her involvement in a civil rights protest. She possesses a beautiful singing voice and a deep love for gospel music. She provides emotional support to the other girls while carefully counting down the days until her eighteenth birthday when she will be legally free.

Born Genesee, Sister Bernadette is a young nun working as a bookkeeper at the Home of the Good Shepherd. Having grown up in poverty and neglect, she views the institution's strict discipline as a source of stability and security. Her natural compassion occasionally conflicts with the rigid enforcement of the older nuns' rules.

Fiona is Mairin's best friend from St. Wilda’s school. Coming from a large, chaotic Irish Catholic family, her life is derailed when she becomes pregnant at fifteen. She is sent away to conceal her situation, experiencing firsthand the harsh social penalties imposed on young women who stray from societal expectations.

Deirdre is Mairin and Liam's mother, an Irish immigrant who rigidly adheres to Catholic doctrine. She lives in fear of financial ruin and social judgment, which heavily influences her marriage to Colm and her decisions regarding her children. She carries unhealed wounds from her past experiences in Ireland.

Flynn is Fiona's older brother, a reliable young man who drives a produce truck. He is protective and steady, offering Mairin his phone number in case she ever needs help. He provides a sharp contrast to the aggressive men in Mairin's life through his calm and supportive demeanor.

Liam is Mairin's eighteen-year-old brother who has recently been drafted into the Vietnam War. He is patient, protective, and serves as a vital mentor to Mairin. He actively defends his sister against their stepfather and teaches her self-defense tactics before he leaves for deployment.

Everly is an adult woman attempting to trace her origins through sealed government records. Raised in a loving adoptive family after being born in Buffalo, she faces bureaucratic dead ends in her quest to understand her history.

Sister Rotrude is an older nun who enforces the strict discipline of the Good Shepherd. She readily utilizes physical force, slapping girls for perceived disrespect, and refuses to listen to any complaints about the staff's behavior.

The Mother Superior oversees the Home of the Good Shepherd. While she projects an image of pious charity to the outside world, she secretly conceals cash payments from the diocese and enables the abuse occurring within her walls.

Denise is a white teenager who entered the Good Shepherd from the foster care system. She initially acts as a bully to mask her own trauma, but she gradually drops her defenses as the girls build solidarity against the nuns.

Janice is a teenager placed in the Home because her family could not financially support all their children. She is desperate to find a place where she belongs, which sometimes leads to clumsy interactions with her peers.

Kay is a ward of the state who has developmental disabilities. She finds brief moments of joy in caring for a small mouse, but her innocence makes her particularly vulnerable to the nuns' harsh punishments.

Kevin is a local boy in the Fruit Belt who serves as an altar boy at the Catholic church. He is Mairin's early romantic interest, representing the normal teenage life she is suddenly forced to leave behind.

Miss Adler is a librarian and a Holocaust survivor who provided Angela with literature about same-sex relationships, offering the young girl a rare source of acceptance and understanding before her institutionalization.