Meredith, known to her family as Merry, is a twenty-three-year-old woman who lived through the filming of a reality documentary about her sister's psychological deterioration. During her childhood, she frequently demands attention and heavily inserts herself into the dynamics of her struggling family. In the present, she provides interviews for an upcoming book about the events, relying on her admittedly compromised and trauma-clouded memories. She now lives in a Boston condo purchased with proceeds from the television show.

Marjorie is a fourteen-year-old girl experiencing acute onset paranoia, psychosis, and auditory hallucinations. Her increasingly distressing behavior leads her parents to seek psychiatric help, followed by spiritual intervention. She is highly perceptive about her family's dysfunction and recognizes the financial toll her condition takes on the household. She occasionally tells her younger sister unsettling stories while struggling to maintain her grip on reality.

John is the father of Meredith and Marjorie. Recently unemployed after working at a toy factory for nineteen years, he struggles with feelings of inadequacy as his family faces foreclosure. He begins attending a local Catholic church secretly, eventually demanding a religious exorcism for his daughter. His rapid descent into religious extremity adds significant stress to an already tense household.

Sarah works full-time as a bank teller while facing the imminent foreclosure of the family home. She initially advocates for treating Marjorie's condition through traditional psychiatric care rather than religious rituals. The crushing weight of impending financial ruin and her husband's intense pressure eventually force her to accept the presence of a documentary crew in her home.

Rachel is a nonfiction author researching a book about the infamous documentary surrounding the Barrett family. She conducts extensive interviews with Meredith to separate reality from sensationalized television broadcasts. She listens carefully to Meredith's disjointed memories while attempting to construct a factual narrative of the historical events.

Dr. Hamilton is the secular psychiatrist initially tasked with treating Marjorie's sudden mental health decline. He prescribes medication and conducts regular therapy sessions. His medical approach is eventually challenged and sidelined by John's preference for religious intervention.

Father Wanderly is a local Catholic priest whom John consults regarding Marjorie's condition. He views Marjorie's illness strictly through a religious lens and advocates for an exorcism. He is instrumental in bringing the television crew to the house, intertwining spiritual intervention with public broadcasting to fund his struggling parish.

Ken is a writer for the reality documentary filming the Barrett family. He frequently interacts with young Meredith, indulging her desire for attention by providing her with a handheld camera. He is one of the more approachable members of the production team and occasionally expresses sympathy for the negative public attention the family receives.

Barry is the executive producer of the reality show filming the Barretts. He manages the production crew, directs the staging of the documentary, and focuses entirely on creating dramatic television out of the family's private crisis.

Dr. Navidson is a professional brought in by the church to evaluate Marjorie and rule out strictly medical causes for her behavior. He interviews her alongside Father Wanderly to determine if she meets the ecclesiastical criteria for an official exorcism.

Father Gavin is a younger priest assigned to assist Father Wanderly during the exorcism process. He is present to help manage the physical and spiritual demands of the intense ritual in Marjorie's freezing bedroom.