Caitlin is a sixteen-year-old high school student who has spent her life in the shadow of her highly successful older sister. Following her sister's sudden departure, Caitlin struggles to define her own identity within her family and community. She joins the cheerleading squad to please her mother and signs up for a local photography class. Her desire to break away from community expectations eventually draws her toward a rebellious crowd.

Rogerson is a wealthy prep school student who drives a BMW convertible and spends his free time selling marijuana. He stands out in the suburban community with his enigmatic demeanor and academic brilliance, often showing little regard for peer conventions. Despite his attractive exterior and ability to impress adults with trivia knowledge, his secretive lifestyle and tense home life hint at underlying anger.

Cass is Caitlin's older sister, previously known throughout her community as a popular athlete and student body president who achieved perfect grades. Her abrupt decision to abandon her Yale acceptance and run away with her boyfriend creates a massive void in the household. She leaves behind a dream journal as a parting birthday gift for Caitlin.

Mrs. O’Koren is a suburban mother heavily invested in maintaining appearances and celebrating academic success. She fixates entirely on her older daughter's achievements, leaving little room to acknowledge Caitlin's individuality. Following the family crisis, she copes by obsessively watching television shopping channels and micromanaging Caitlin's new cheerleading schedule.

Mr. O’Koren is a university dean who handles young adult issues professionally but finds himself unmoored by his own daughter's rebellion. He reacts to the household stress by throwing his energy entirely into his work. This avoidance creates emotional distance from his wife and remaining child.

Rina is Caitlin's best friend at high school. She actively pushes Caitlin to participate in typical social activities, convincing her to try out for the cheerleading squad. She frequently dates athletes and tries to maintain a connection with Caitlin even as their social circles begin to drift apart.

Boo, whose real name is Katherine, is the O’Korens' eccentric and artistic neighbor. She serves as Caitlin's namesake and pays close attention to the teenager's individual needs. Unlike Caitlin's parents, Boo encourages her to pursue unconventional interests like photography.

Stewart is Boo's quirky husband and an artist living next door to the O’Korens. He provides a stabilizing adult presence in the neighborhood. He occasionally offers the O’Korens alternative perspectives on teenage rebellion, drawing on his own history of taking Boo away from her family when she was eighteen.

Corinna is an older teenager who dates one of Rogerson's regular customers. She lives in a small house outside of town and frequently talks about her desire to move to California. She provides Caitlin with a rare, non-judgmental space away from high school pressures.

Dave is Corinna's boyfriend and a regular buyer of marijuana. He lives in a small house where Caitlin and Rogerson frequently hang out. He shows little interest in his girlfriend's dreams of escaping to the West Coast.

Mike is a running back for the high school football team. He attempts to formally date Caitlin by offering her his varsity letter jacket at a party. He represents the conventional, popular path that Caitlin ultimately rejects.

Mrs. Biscoe is Rogerson's mother and a famous, wealthy local realtor. She focuses heavily on maintaining a perfect, superficial image for her family. She willfully ignores the hostile and abusive dynamics occurring within her own household.

Mr. Biscoe is a pharmacy CEO and Rogerson's father. He maintains strict expectations for his son's behavior. He enforces his rules through severe physical discipline behind closed doors in their pool house.

Adam is Cass's boyfriend, whose relationship with her prompts the older sister to abandon her college plans. He eventually works alongside Cass as a staff member on a low-quality television reality show.

Matthew is the instructor for the local photography class that Caitlin takes with her mother and Boo. He recognizes Caitlin's natural talent for capturing expressive portraits. His professional encouragement inadvertently triggers jealousy from Caitlin's boyfriend.

Dr. Marshall is a therapist at the Evergreen Care Center. She assists Caitlin in processing her emotional trauma and drug use, encouraging her to narrate her experiences in a nonlinear, comfortable format.

Jeff is Rina's boyfriend. He occasionally acts as a reluctant driver for Caitlin when her friendship with Rina creates logistical conflicts, such as during a tense trip to a lake house.

Eliza is a high school cheerleader on the same squad as Caitlin. Her quick reflexes allow her to catch Caitlin and prevent a severe injury when the top of their cheerleading pyramid collapses.

Lindsay is a high school cheerleader. She suffers a broken nose when the squad's pyramid formation falls apart during the biggest football game of the year.

Kelly is a member of the high school cheerleading squad. She stops at a car wash to clean out her vehicle before heading to a team party, a detour that inadvertently sets up Caitlin's first encounter with Rogerson.