Catherine is a twelve-year-old girl who spends her summer break looking after her autistic brother. As an avid artist, she uses drawing to cope with feelings of isolation and to communicate with others. She longs for a normal summer and creates an extensive list of rules to help her brother navigate social situations. Though responsible, she struggles with feeling overlooked by her busy parents.

David is Catherine's eight-year-old brother who has autism. He attends an occupational therapy clinic and loves trips to the local video store. He relies heavily on routines and learns how to navigate the world through the written rules his sister provides for him. Sensitive to loud sounds, he often covers his ears during rainstorms or loud events.

Jason is a teenage boy who uses a wheelchair and attends the same occupational therapy clinic as David. Being non-speaking, he communicates using a binder filled with written word cards. He is highly observant, loves music, and desires greater independence and more expressive ways to share his thoughts with the world.

Kristi is Catherine's new neighbor, a stylish and perfectly groomed girl of the same age. She is new to the coastal Maine community and trying to navigate the emotional weight of her parents' recent separation. She focuses heavily on fashion, teen magazines, and boys, hoping to fit in quickly and find a summer romance.

A work-from-home tax preparer who balances her career with managing her son's intensive occupational therapy. She relies heavily on Catherine to babysit, often expecting her daughter to be completely self-sufficient while she focuses her attention on David's immediate daily needs.

A pharmacist who works long hours and frequently arrives home late. He struggles to engage with his family's daily emotional challenges, often retreating into his career or his backyard tomato garden. He maintains a specific routine of taking his son to the video store but neglects spending one-on-one time with his daughter.

Jason's mother, a fiercely protective parent who constantly accompanies her son to his therapy sessions. She manages his communication book and tries to ensure he is treated with respect, though she sometimes struggles to recognize his growing desire for independence.

A neighborhood boy who lives at the end of Catherine's street. He frequently mocks David and exploits his autism for cruel amusement, making him a constant source of anxiety and anger for Catherine. He hangs out with Kristi, complicating Catherine's desire to befriend her new neighbor.

Kristi's mother, who has recently separated from her husband and moved to the coastal Maine village. She maintains a neat, fashionable home and tries to settle into her new life while raising her teenage daughter.

Catherine's best friend who spends her summers in California with her father. Her three-month absence leaves Catherine feeling deeply lonely and desperate for a new friend to share her summer with.

The occupational therapist who works with David at the clinic. She guides his treatment sessions and helps him develop coping strategies and behavioral skills.

Jason's older brother. He is present at the family home and casually interacts with Catherine, demonstrating a passing familiarity with Jason's communication book and the new cards Catherine draws.

One of Catherine's pet guinea pigs. Nutmeg provides Catherine with comfort and serves as a bridge for connection when Catherine brings her to the clinic to meet Jason.

Catherine's other pet guinea pig. Along with Nutmeg, Cinnamon is a source of joy and amusement for Catherine, who shares stories about their antics to entertain her friends.