Mason is a twelve-year-old middle school student who lives in a crumbling house on his family's apple orchard in Merrimack. He copes with learning disabilities, excessive sweating, and synesthesia while grieving the recent accidental death of his best friend. Physically the largest boy in his class, he serves as a frequent target for neighborhood bullies. Despite these challenges, Mason is gentle, deeply loyal, and eager to document his experiences using a voice-to-text program.

Ms. Blinny is the school social worker whose office, decorated with pink paint and glitter, provides a sanctuary for struggling students. She is a messy, cheerful, and crafty professional who constantly drops glitter wherever she goes. She introduces Mason to a voice-to-text software called the Dragon, empowering him to tell his own story.

Benny is Mason's best friend from first grade who died in a fall from a tree fort ladder on the Buttle property before the novel begins. His memory heavily influences Mason's daily actions and emotional state. Benny was adopted by his two fathers and bonded with Mason over their shared feeling of being different from the other children.

Uncle Drum is Mason's uncle who took over guardianship duties after Mason's father left and his mother died. Following successive family tragedies and bad crop yields, Uncle Drum sold off sections of the family orchard to developers and largely stopped working. He spends most of his days sitting at a diner, maintaining a quiet but protective presence over his nephew.

Grandma is the matriarch of the Buttle family who lives in the run-down farmhouse with her son, grandson, and a houseguest. She previously worked as a teacher's aide for special needs children but quit following successive family tragedies. She is welcoming and warm, readily accepting Calvin into their home and maintaining household routines.

Calvin is a highly intelligent, physically small boy with white-blond hair who recently moved into a new housing development built on former Buttle orchard land. He carries a tablet to research new topics, architecture, and historical sites. He forms an immediate bond with Mason, looking past physical differences to focus on building a safe fortress in the old root cellar together.

Matt Drinker is a neighborhood bully who frequently targets Mason and the new boy, Calvin. He uses lacrosse balls and apples as projectiles to harass the boys on their way home from the bus stop. Despite his aggressive behavior toward peers and his own dog, he displays a conflicting inner insecurity when left alone at his house.

Andy is one of Benny's two fathers and a carpenter by trade. Before his son's death, he used to build projects with Mason and Benny around the neighborhood. Following the tragedy, Andy struggles intensely with grief, finding it emotionally painful to even look at Mason.

Lieutenant Baird is the local police officer assigned to investigate the tragic accident at the tree fort. He visits the Buttle household frequently, pressing Mason for tiny details about the incident. He approaches the case with intense suspicion, persistently believing that there is more to the story than Mason reveals.

Shayleen is a young woman who recently moved into the Buttle home, taking over Mason's old bedroom. Uncle Drum brought her to the farmhouse after finding her upset and unable to pay for her meal at a diner. She spends most of her time indoors watching television, ordering items from home shopping networks, and nagging the family.

Mrs. Drinker is Matt's mother and the Buttles' neighbor. Her husband frequently travels for work, leaving her home alone with her son and their dog. She shows kindness to Mason, checking on his safety during a sledding accident and hiring him for pet care, but she struggles to keep her son's aggressive behavior in check.

Moonie is the Drinker family's pet dog. He is a sweet-natured escape artist who frequently runs away from his own yard to seek out Mason. Mason deeply loves Moonie and enjoys watching him, offering the dog the care and affection that he lacks at home.

Annalissetta is a confident middle school student with cerebral palsy who uses a green walker she calls a Crocodile. She shares dictation software with Mason and serves as a strong model of self-advocacy, teaching Mason not to underestimate her capabilities.

Corey is one of the popular boys who hangs out with the local bullies. However, he is notably more reasonable and compassionate than his friends. He attempts to stop the extreme bullying when it goes too far and shows subtle signs of friendliness toward Mason.

Franklin is Benny's other adoptive father and Andy's partner. Like Andy, he struggles profoundly with the sudden loss of his son. When Mason approaches the family at the local diner, Franklin firmly asks the boy to leave them alone, unable to cope with the reminder of his child.

Lance is a lacrosse player and a close sidekick to the neighborhood bully. He actively participates in harassing Mason and Calvin, using his sports equipment to launch apples and balls at them. He heavily follows Matt's lead in neighborhood conflicts.

Margie is the housekeeper for the Chumsky family. She is highly protective of Calvin and views Mason with a clear, uncomfortable attitude that Mason notes as a face of pity and judgment, reflecting the neighborhood rumors.