Nora is a 37-year-old successful general surgeon living in Mountain View, California. She changed her last name to distance herself from her father's notorious criminal past. She is highly dedicated to her medical career, using her ability to save lives as a counterbalance to her family history. She actively avoids romantic attachments and keeps her social circle exceptionally small.

Aaron is Nora's father, currently serving life in a maximum-security prison for the murders of at least 30 women. Prior to his arrest, he worked as a phlebotomist and presented himself to the world as a charming, handsome family man. He used his woodworking hobby in the locked basement as a cover for his violent activities, masking the odors with strong lavender cleaning supplies.

Brady is a bartender at Christopher's dive bar who previously dated Nora during their college years. Currently working in the service industry while between tech jobs, he has physically and emotionally matured since their first relationship. He is polite and attentive, offering Nora a patient connection despite her intense reluctance to let anyone close to her.

Harper is a capable and attractive woman in her twenties who works at Nora's private medical practice. She is highly organized and reliable, keeping the clinic's schedule running smoothly. She demonstrates a strong ambition to advance her education, actively studying biology textbooks during her breaks with hopes of pursuing a medical career.

Philip is Nora's medical and business partner at their private practice. Unlike the frugal and reserved Nora, he is flashy, outgoing, and drives a red sports car that Nora considers a sign of a midlife crisis. Following a difficult divorce, he dates frequently and openly flirts with younger women in the clinic and hospital.

Linda is Nora's mother and Aaron's wife. She tries to maintain a traditional, normal household but is frequently subjected to her husband's cruel remarks about her physical appearance. She frequently argues with Aaron regarding Nora's unusual behavior and need for therapy, while intentionally ignoring the strange noises coming from their locked basement.

Ed is a police detective investigating the recent murders of young women in the area. Described as having close-cropped hair and shrewd, observant eyes, he is persistent in his inquiries. He frequently questions Nora, whose severe, trauma-induced aversion to police officers makes their interactions highly strained.

Marjorie is an awkward, overweight, and lonely classmate of Nora's during her childhood in Oregon. She frequently walks home alone to an empty house on an abandoned trail, making her a frequent target for the bullying behavior of her peers.

Henry is a former patient of Nora's who develops an uncomfortable and persistent fixation on her. His aggressive advances and refusal to accept rejection make Nora feel deeply unsafe, prompting her to take active defensive measures against him.

Arnold is one of Nora's surgical patients. He complains loudly about wait times at the clinic while hiding his abusive nature. Nora strongly suspects him of physically harming his wife after observing her injuries during a medical consultation.

Mrs. Kellogg is the wife of Arnold Kellogg. She defensively denies being abused when Nora privately asks her about her facial injuries, though her situation deeply troubles the surgeon.

Amber is a former patient of Nora's who possesses dark hair and blue eyes. Her gruesome murder mimics the exact pattern of Aaron Nierling's historical crimes, drawing heavy police attention directly to Nora's medical practice.

Mrs. Swanson is the grieving and furious mother of Amber Swanson. She tracks Nora down at her medical practice to aggressively accuse her of being involved in her daughter's death, threatening to take her suspicions to the media.

Shelby is another of Nora's former patients who shares the specific physical characteristics of Aaron Nierling's historical victims. Her subsequent death dramatically escalates the police investigation into Nora and her clinic.

Mrs. Chelmsford is Brady's elderly, skeletal landlady. She frequently sits on the porch and issues disturbing, paranoid warnings to visitors about hearing screams at night, though her family claims she is simply confused due to her age.

Patricia is Nora's newly hired attorney. She provides legal counsel to help Nora navigate the intensifying police investigation surrounding the brutal deaths of her former patients.

William is a man who crashes his vehicle on a winding road while aggressively tailing Nora's car at night. Nora later visits him in the hospital, recognizing his face but remaining unable to immediately place his identity.

Ruby is Brady's five-year-old daughter. Her existence is initially kept hidden from Nora due to the casual, uncertain nature of Brady's early dating life.

Sheila is a medical assistant working alongside Nora and Harper at the private surgical practice. She provides emotional support to her colleagues and helps maintain the daily operations of the clinic.

Sonny is Harper's boyfriend. He breaks up with her unexpectedly instead of proposing, leaving her deeply distressed and tearful during her shift at the medical clinic.

Tiffany is a childhood friend of Nora's in Oregon. She actively participates in teasing and throwing spitballs at awkward classmates, representing the casual cruelty of Nora's childhood social circle.