The titular character whose posthumous journal entry influences Martha, leaving a lasting impact on her journey and goals.

Martha’s wise, understanding grandmother, with whom she forms a strong bond during her summer stay in Cape Cod.

A boy Martha initially develops a romantic interest in, who later becomes a source of conflict for her.

Jimmy's brother, seen as honorable and trustworthy by Martha, who provides support in contrast to Jimmy’s deceptive actions.

Martha’s older brother, who provides humor and sibling rivalry, yet shares close bedtime conversations with her.

Martha’s father, who has shifted from being a lawyer to a stay-at-home dad trying to write a novel.

Martha’s mother, whose relationship with Martha can be intense, swinging rapidly between love and frustration.

Martha’s two-year-old sister, representing consistency in the family and playing a role in Martha's introspective moments.