Jeremy is a twelve-year-old boy living in New York City who is one month away from his thirteenth birthday. Since his father's sudden death five years ago, he has grown cautious and relies heavily on predictable daily routines to feel safe. When he receives a mysterious locked box from his late father, he forces himself to leave his comfort zone and search the city for the missing keys.

Lizzy is Jeremy's bold, adventurous best friend. She is naturally messy but shows unusual care when handling the special box left by Jeremy's dad. Over the summer, she begins exploring new interests like makeup and hanging out with new neighbors, causing some friction as she figures out who she wants to be.

Mr. Oswald is a wealthy antique collector and pawnshop owner in New York City. He travels in a private limousine and tasks Jeremy and Lizzy with delivering specific items to people around the city as part of their community service. He acts as an enigmatic guide, offering the children glimpses into the lives of diverse New Yorkers.

Jeremy's father died in a car accident five years before the events of the story. During his life, he operated under the belief that his time was limited, prompting him to live fully and savor his experiences. He carefully arranged for Jeremy to receive a special locked box containing his thoughts on the meaning of life.

Jeremy's mother works to provide a stable life for her son in New York City. She understands the emotional weight of her late husband's gift and encourages Jeremy's search, though she firmly enforces rules when his investigations lead to trouble.

Jeremy's grandmother lives in New Jersey and hosts Jeremy and Lizzy late in the summer. She is enthusiastic about family traditions and expects the children to participate in the local young talent contest, signing them up for a hula hoop routine.

A girl around Jeremy and Lizzy's age who recently moved into their building. She quickly connects with Lizzy over shared interests like makeup and seances, representing the changing social dynamics in Lizzy and Jeremy's friendship.

The brother of the new neighbor girl. His casual interactions with Lizzy cause her to blush, marking her growing interest in romance and leaving Jeremy feeling confused by her reaction.

A round, red-faced policeman who discovers Jeremy and Lizzy trespassing in the lawyer's old office. Instead of arresting them, he assigns them to work off their punishment by helping a local pawnshop owner pack up his store.

A local merchant who runs the neighborhood lock shop. He provides Jeremy and Lizzy with a large box of old keys to test against the wooden box and listens to Jeremy's concerns about the approaching birthday deadline.

The recipient of the children's first delivery assignment. She receives a copy of a Winnie-the-Pooh book she pawned during her youth to buy a dress, a decision that ultimately cost her a childhood friendship.

A youthful, upbeat man who pawned a lamp as a teenager to buy a watch. He has since abandoned his materialistic desires in favor of a simple life, and his contented outlook triggers a crisis of purpose in Jeremy.

A researcher who receives his grandfather's pawned telescope from Jeremy and Lizzy. He pawned the item at age fifteen to buy a track uniform, which helped him secure a college scholarship and build his current career.

A woman living in Atlantic City who explains the history of her grandmother's fortune-telling business. She provides Jeremy with crucial context about the prophecy his father received decades earlier.

Mr. Oswald's grandfather, who ran the family pawnshop during the 1930s and 1940s. He made deals with neighborhood children, allowing them to pawn their belongings while secretly keeping the items safe rather than selling them.

A merchant selling a wide variety of locks and keys at the flea market. He and his wife give Jeremy a unique key to keep after the children test their stock against the wooden box.