Bet is an exhausted single mother raising her nine-year-old developmentally disabled son alone after her husband's departure. She carefully curates Arnold's outward appearance for a tense train trip, using tidiness as a coping mechanism. This rigid behavior masks her deep insecurities and fears of societal judgment. She secretly yearns to be seen as an individual rather than solely defined by her maternal responsibilities.

Arnold is a nine-year-old boy with a developmental disability that renders him non-verbal. He communicates through grunts and physical gestures, relying entirely on his mother for daily care. Though he appears small, he possesses significant physical strength that is becoming increasingly difficult for his caretakers to manage. He finds comfort in familiar objects, such as his outgrown red corduroy jacket and favorite peanut butter cookies.

Avery is an ordinary, stocky man who struggles with the realities of fatherhood. He becomes deeply unsettled when doctors confirm Arnold's developmental disability. Unwilling to process his self-doubt and fear with his wife, he completely withdraws from the family.

Bet's father is an industrious fisherman from Salt Spray, Maryland. He loves the ocean and builds his family's schedule around water and weather patterns. He attempts to teach his daughter how to bodysurf to instill his own ability to manage unpredictable forces.

Mrs. Puckett is a soft-spoken woman who served as Arnold's babysitter for many years. She recently quit her position because she could no longer manage the boy's growing physical strength. She maintains a degree of affection for him, baking his favorite cookies as a parting gift.

The nurse is a staff member in a shapeless gray uniform working at a large facility at the end of Bet's journey. She operates strictly according to institutional protocols. She handles visitors with a detached, impersonal demeanor.

The taxi driver takes Bet and Arnold to their destination after they disembark from the train. He attempts to make polite conversation during the drive. He responds casually to Bet's anxious and repetitive requests.

The train conductor disrupts the quiet car by loudly harassing a Black passenger about a ticket. His aggressive behavior inadvertently provides a distraction that amuses Arnold. This sudden commotion relieves Bet's immediate anxiety about her son having a tantrum.

The local mayor sets up a makeshift stage in a vacuous train station to deliver an impromptu speech. His sudden appearance provides a timely distraction for the waiting travelers.