Alex is a boy living in New Jersey who loves airplanes and desperately wants a pet dog. Initially focused heavily on his own wants and frustrated by his parents treating him like a child, the unusual events of his birthday challenge him to take on real responsibilities. He often makes imaginary deals with the universe in hopes of controlling his circumstances.

Mac is an older gentleman who lives in the neighborhood near Alex. A former aviation enthusiast who built model airplanes with his son, he now spends his days caring for his ailing wife. When community emergencies arise, he provides guidance and a safe haven for neighborhood children.

Jordan is a school bully who relentlessly torments Alex and other classmates. He uses physical intimidation and cruel insults to assert power over his peers. His aggressive behavior stands in sharp contrast to the kindness shown by others in the community.

Alex's father works as a commuter train driver, traveling daily beneath the Hudson River to the World Trade Center in Manhattan. He sets strict rules for his son regarding household chores and schoolwork. He loves his family deeply and expects his children to demonstrate maturity.

Alex's mother works as a nurse at a local hospital. She balances demanding shifts with managing her household, often urging her son to act his age. During community emergencies, her professional duties require her to remain at the hospital to care for patients.

Nunu is Alex's six-year-old sister who carries her favorite doll, Lolly, everywhere. She is innocent and frequently asks questions about the world around her. When their parents are unavailable, she relies heavily on her older brother for guidance.

Radar is a playful stray dog who immediately bonds with Alex. Despite carrying injuries and lacking a home after his previous residence on Van Orton Street burned down, he exhibits a fun and feisty personality. He eventually takes on a fiercely protective role toward his new companions.

Doug is one of Alex's closest friends from school. He shares interests in video games and baseball, though he occasionally avoids conflict when local bullies approach the playground.

Kwan is part of Alex's close-knit social circle. He joins the other neighborhood boys in playing baseball at the local park.

Calvin is a sidekick who usually goes along with bullying activities around the neighborhood. However, he shows unexpected flashes of conscience when situations escalate beyond harmless teasing.

Deemer is a loyal follower of the local school bully. He actively participates in the intimidation of other students and helps chase classmates through the park.

Dottie is Mac's wife, who is battling Alzheimer's disease. She spends her time watching cartoons and requires constant care from her husband, remaining entirely unaware of the unfolding national tragedies.

Bobby is an adult who works in the World Trade Center. He is described by his family as a sweet, kind man who volunteers at soup kitchens and regularly donates blood.

Dr. Marks is a compassionate local veterinarian. He provides free medical care for injuries and helps uncover a stray dog's origins by scanning for a microchip.

Mr. Patel owns a local pizza shop. He demonstrates immense kindness during a community crisis by inventing a fake lunch rebate special so he can give out free food without hurting anyone's pride.

Mrs. Hamlin is a schoolteacher. She abruptly dismisses her class and instructs the students to pack their belongings after receiving news of a local emergency.