Lia is an eighteen-year-old high school senior struggling with anorexia and self-harm. She lives with her father and stepmother after being discharged from an inpatient recovery clinic called New Seasons. To maintain her dangerously low weight, she actively deceives her family by tampering with the scale using quarters sewn into her bathrobe and staging dirty dishes. She feels immense guilt over ignoring Cassie's final phone calls and experiences intense visual and auditory hallucinations of her deceased friend.

Cassandra Jane Parrish is Lia’s childhood best friend who dies alone in a motel room at the start of the story following a battle with bulimia. Cassie was a daring, imaginative girl involved in drama and soccer. In middle school, she and Lia swore a blood oath to be the skinniest girls in their school. Following her death, Cassie appears to Lia as an intrusive, ghostly presence who encourages dangerous behaviors and feeds on Lia's guilt.

David is Lia’s father, a highly successful history professor and author who occasionally consults on national news shows. He travels frequently for his academic work and struggles to connect with his teenage daughter, often buying her gifts meant for young children. He prefers to believe Lia is healthy and resists acknowledging the persistent severity of her eating disorder.

Dr. Marrigan is Lia’s mother and a practicing cardiologist. She previously pressured Lia to follow a prestigious Ivy League and medical school track. She treats Lia’s illness with a clinical, commanding approach, causing Lia to feel treated like a medical specimen rather than a daughter. This friction led Lia to move out and live with her father instead.

Jennifer is Lia’s stepmother, who attempts to manage Lia’s recovery within their home. She enforces Lia's meal plans and conducts weekly weigh-ins on a scale in the bathroom, though she is easily manipulated by Lia's tricks. She is fiercely protective of her young daughter, Emma, and tries her best to maintain a functional family environment despite David's absences.

Emma is Jennifer’s third-grade daughter and Lia’s stepsister. She participates in soccer, basketball, violin, and French lessons. Emma's innocent presence offers Lia a rare sense of peace and sisterly affection in the household, and she enjoys snuggling with Lia to watch movies.

Elijah is a young man living in room 115 of the Gateway Motel, the same building where Cassie was found dead. He has thick black hair, wears black-rimmed glasses, has a plug in his earlobe, and sports a tattoo of a bike messenger god. He works on his car, collects books, and plans to leave on a winter road trip.

Dr. Nancy Parker is Lia’s assigned therapist. She attempts to help Lia process her eating disorder and Cassie's death. Lia views her with extreme suspicion, believing the therapist simply wants to manipulate her thoughts and put her in an easy diagnostic box.

Cindy is Cassie's mother. She lives across the street from Dr. Marrigan and keeps a rose garden where the girls once buried a pet mouse. Following her daughter's tragic death, she desperately seeks answers and tries to contact Lia for closure.