Trent is a 12-year-old boy entering sixth grade who carries a heavy emotional burden after a fatal hockey accident involving his teammate. He expresses his volatile emotions as a physical fire burning in his chest and channels his anxiety into a "Book of Thoughts" filled with dark drawings. He struggles to manage his anger, frequently lashing out at teachers and isolating himself from his former friends.

Fallon is a middle school student with a prominent, jagged scar running down her face. She consistently invents unbelievable stories about how she received the injury to deflect unwanted questions. A dedicated cinephile who points out continuity errors in films, she initiates a movie club to spend time with Trent.

Aaron is Trent's 16-year-old older brother who works as a lakeside lifeguard. He acts as a mediating force in the family, frequently driving his younger brothers to events and providing a buffer during tense domestic moments. He attempts to protect his mother from additional stress by handling his own problems quietly.

Doug is Trent's 10-year-old younger brother who shows little interest in playing sports. He enjoys executing elaborate pranks, such as unscrewing saltshaker lids and planting multiple alarm clocks in bedrooms. His growing friendship with Jared's younger sister causes friction at home.

Ms. Emerson is Trent's sixth-grade homeroom teacher. A former home economics instructor, she fills her classroom with old ovens and an extensive collection of potted plants. She maintains a calm, observant demeanor even when students intentionally act out in her presence.

Trent's mother is a hardworking woman employed at a local kitchen store. She worries deeply about Trent's emotional state and his deteriorating relationship with his father. She tries to offer guidance and a sympathetic ear during his moments of intense anger.

Trent's father shares custody of his three sons and expects them for awkward dinners three times a week. He frequently loses his temper over Trent's sullen behavior and angry outbursts. Their relationship is severely strained and marked by poor communication.

Kari is Trent's stepmother, currently pregnant with her first child. She navigates the awkward dynamics of her husband's relationship with his sons while anticipating the arrival of her new baby.

Jared is a boy from Trent's community who died of an undiagnosed heart defect after being struck by a hockey puck. His sudden death profoundly impacts the town and serves as the catalyst for Trent's overwhelming feelings of responsibility.

Annie is Jared Richards's younger sister. Following her brother's death, she spends time with Doug Zimmerman but harbors deep resentment toward Trent. She glares at Trent from a distance and participates in minor pranks against him.

Noah is one of Trent's former friends from the neighborhood sports games. He tries to reach out to Trent after the accident but is continuously pushed away. He joins the intramural baseball team coached by his uncle.

Jeremiah is a neighborhood boy who plays pickup sports and works at his father's movie theater. He has a hostile, abrasive personality and frequently antagonizes Trent while mocking Fallon.

Mr. Gorman is the middle school physical education teacher and the coach for intramural baseball. He expects strict participation in his gym classes and does not tolerate students destroying athletic equipment.

Ray is the manager of the local kitchen supply store. He runs a relaxed workplace, allowing baseball games to play on the radio, and maintains a friendly dynamic with his employees.

Clarisse is an older teenager who frequently calls Aaron's phone. Doug suspects she is Aaron's girlfriend, though Aaron is highly evasive when questioned about her presence in his life.

Fallon's father is a local police officer. He is highly protective of his daughter, particularly regarding the peers she chooses to spend time with and the safety of her environment.