Stewart is a highly intelligent, 13-year-old boy who recently transferred from an academy for gifted children to a regular public high school. He grieves the loss of his mother and uses a science-based theory about molecules to understand human connection. He approaches his new blended family with optimism and a desire to fit in, though he struggles with social cues and interpreting peer hostility.

Ashley is a 14-year-old high school student who reigns over the popular crowd. She cares deeply about fashion and maintaining a flawless public image, fiercely guarding her social status. Her parents' recent divorce and her father's coming out leave her embarrassed and defensive, causing her to isolate herself from her new blended family.

Jared is an athletic, wealthy high school student who recently transferred from a private school. He commands the attention of the student body with his good looks and stylish clothes. Beneath his charming exterior, he harbors a cruel streak and targets smaller, less popular students in the locker room.

Leonard is a television news producer and Stewart's father. He works to rebuild his life two years after his wife's passing by moving his household into his girlfriend's home. He possesses a relaxed, messy domestic style that occasionally clashes with his new living arrangements, but he maintains a patient and calm demeanor.

Caroline is a television news anchor and Ashley's mother. She maintains a neat, highly organized postmodern home. She tries to enforce discipline when her daughter misbehaves while attempting to foster a positive environment for her new blended family.

Phil is Ashley's father who works in advertising. Following his divorce from Caroline, he lives in a small laneway house in the backyard of his former family home. He recently came out as gay and tries to maintain a relationship with his daughter despite her constant rejection of his attempts to connect.

Michael is Phil Anderson's new boyfriend. He works in the advertising and film industry. He dresses impeccably and possesses inside connections to the fashion world, which slowly attract Ashley's interest despite her initial determination to dislike him.

Lauren is Ashley's best friend and a member of the popular crowd at school. She is highly attuned to social dynamics and gossip. Ashley views her as both a close companion and a potential threat to her carefully curated reputation.

Phoebe is an intelligent student at Borden Secondary School. She belongs to the Mathletes club and operates outside the popular social hierarchy. She provides Stewart with a welcoming community and warns him about the cruel nature of certain classmates.

Violet is a smart, observant high school student who is friends with Phoebe. She recognizes the toxic social dynamics at her school and states her negative opinions about the popular crowd directly. She eats lunch with Stewart and welcomes him into her friend group.

Alistair is Stewart's best friend from his previous academy for gifted children. He shares Stewart's intellectual interests and visits for weekend sleepovers. He helps Stewart brainstorm practical solutions to the bullying he faces at his new school.

Mrs. Inkster is Stewart's late mother who died two years prior to the events of the novel. Her memory heavily influences her son's daily habits. Her physical belongings, including her favorite afghan and a distinctive painting of her, cause friction in the newly blended household.

Schrödinger is Stewart's pet cat. He provides a crucial source of emotional stability for the grieving teenager. His presence in the new house occasionally causes minor disturbances, but he serves as a comforting figure to multiple household members.

Dr. Moskovich is Stewart's therapist. She listens to his frustrations regarding his new living situation. She helps him process his ongoing grief over the loss of his mother and adjust to his new environment.

Paolo is a high school student and a close friend of Jared. He follows Jared's lead in social situations. He participates in the school's exclusionary social culture by backing up his friend.