Isabelle is a 17-year-old high school senior who goes by Izzy. Living in the foster care system after a traumatic family event, she assists her foster mother with a museum project cataloging the suitcases of former psychiatric patients. She is highly observant but lives in fear of her own genetics, worrying she might develop a mental illness.

Clara is an 18-year-old heiress growing up in a wealthy New York household in the late 1920s. Spirited and rebellious, she prefers flapper culture to the restrictive expectations of her upper-class parents. After refusing an arranged marriage, she is committed to a psychiatric institution by her controlling father. She deeply loves Bruno, a working-class Italian immigrant.

Joyce is Isabelle's biological mother. She resides in a state prison after shooting her husband. Her actions deeply traumatized her daughter, leading to Isabelle's placement in the foster care system. She writes frequently to Isabelle from prison. Isabelle fears opening the correspondence because she worries about inheriting mental illness.

Peg is Isabelle's current foster mother and a museum curator. She has the appearance of a free-spirited hippie and catalogs the abandoned suitcases of former psychiatric patients for a historical project. She provides Isabelle with a stable, supportive home environment. She actively encourages her foster daughter's interest in history and research.

Ethan is a high school student with raven-black hair and light blue eyes. He helps his father, Peter, with photography for the Willard suitcase project. He dates the school's primary bully, Shannon. He frequently shows kindness to Isabelle, creating friction within his social circle. He aspires to work in the medical field as an emergency responder.

Shannon is a popular blonde high school student who perceives Isabelle as a threat. As Ethan's girlfriend, she is highly territorial. She orchestrates increasingly cruel bullying campaigns against Isabelle to reassert her social dominance. She hides a difficult home life behind her aggressive exterior.

Henry is Clara's father and a wealthy owner of Swift Bank. Deeply concerned with status and wealth, he acts as an authoritarian figure in his household. He aggressively polices his daughter's life, determined to control her future and squash any rebellion against his business interests.

Bruno is a working-class Italian immigrant who works as a longshoreman. He falls deeply in love with Clara after meeting her at a dance club. Despite the intense disapproval of Clara's wealthy father, Bruno remains fiercely devoted to her and attempts to build a life together.

Dr. Roach is a small, wiry physician at the Willard facility who wields immense power over the patients. He treats his female patients with profound disrespect. He utilizes brutal psychiatric treatments as forms of punishment rather than medical care.

Harry is the art director for the state museum and Peg's husband. Together with Peg, he acts as Isabelle's foster parent. He treats Isabelle with steady kindness, creating the safest and most supportive home environment she has experienced since entering the foster system.

Alex is a well-dressed Lakeshore High School student who befriends Isabelle. Having previously been part of Shannon's inner circle, she understands the social dynamics of the school and acts as a guide and protector. She harbors a strong interest in the paranormal.

Josh is the star linebacker of the high school football team and Shannon's former boyfriend. He remains devoted to Shannon and willingly executes her cruel pranks. He uses his physical size to intimidate other students.

Dave is a high school student who dates Crystal and runs in Shannon's social circle. He eagerly participates in the group's malicious activities and assists Josh in carrying out physical bullying against Isabelle.

Crystal is one of Shannon's close friends and loyal followers. She actively participates in bullying Isabelle, performs Shannon's bidding without question, and leads a mock seance on the grounds of the abandoned asylum.

Luke is a high school student and part of Shannon's extended friend group. He participates in the group's late-night excursions. He is characterized by his fear of being perceived as gay, which dictates his reactions during their pranks.

Ruth is Clara's mother and the heiress to the Bridge Bros. Clothing Emporium. Devastated by the death of her son William, she largely removes herself from the discipline and schooling of her remaining child. She defers entirely to her husband's harsh judgments.

Rita Trench is a physically imposing nurse at the Willard facility. She rigorously enforces the institution's harsh rules and demands complete obedience from Clara. However, she shows occasional flashes of humanity that distinguish her from the more openly cruel staff members.

Nurse May is a staff member at the Willard facility who uses her proximity to Dr. Roach to act superior to other nurses. She openly flirts with the doctor and treats patients like Clara with hostility. She readily exposes their private medical information to cause trouble.

Esther is a beautiful blonde patient at Willard who becomes friends with Clara. Committed to the institution by her husband merely for kissing another man, she represents the systemic ease with which independent women are institutionalized.

Madeline is a petite woman in her mid-twenties who was admitted to Willard after leaving an abusive husband. She befriends Clara and Esther. She bonds with them over the shared trauma of being institutionalized for challenging the men in their lives.

Matilda is a patient with a thick European accent who works in the laundry facility. She provides a rare source of physical comfort on the ward by giving daily hugs to the other women.

Lawrence is a patient at Willard who works as the facility's gravedigger. Living in a run-down shack on the property, he is a compassionate man. He quietly makes wooden cross markers for the deceased patients so they will not be forgotten in unmarked graves.

Susan is a retired kindergarten teacher whom Peg and Isabelle seek out during their research into the Willard suitcases. Raised by adoptive parents who refused to discuss her origins, she spent much of her life fearing she carried a genetic predisposition for mental illness.

Nurse Yott is a staff member at the private Long Island Home for Nervous Invalids where Clara is first committed. She shows a rare flash of sympathy for Clara's predicament. She quietly agrees to help Clara communicate with the outside world.

Dr. Thorn is the admitting physician at the Long Island Home for Nervous Invalids. He dismisses Clara's explanations of her father's coercion as signs of paranoia. He eventually oversees her transfer to a state institution.