Calpurnia is an inquisitive eleven-year-old girl living in rural Texas in 1899. Fascinated by the natural world, she prefers catching scientific specimens and observing animals over learning traditional domestic skills like knitting and cooking. Her curiosity drives her to forge a unique bond with her grandfather to study the local environment. She constantly feels at odds with her family's expectation that she will eventually become a traditional debutante.

Walter is a Civil War veteran and an avid natural scientist who spends most of his time isolated in his laboratory and library. Having corresponded with notable scientists, he possesses a wealth of knowledge about the natural world that he begins to share with his eager granddaughter. He views scientific progress as an inevitability and encourages Calpurnia to question the world around her.

Margaret is the matriarch of the Tate family who strictly adheres to the traditional southern expectations of womanhood. Having missed her own opportunity to formally debut in society due to the Civil War, she earnestly desires for her only daughter to master household management and become a proper debutante. She grows increasingly concerned by Calpurnia's interest in the natural world and attempts to correct her behavior with mandatory cooking and knitting lessons.

Harry is the eldest of the Tate siblings at seventeen years old. He initially supports his younger sister's interests by gifting her supplies, though his attention shifts as he enters the social world of courting young women. He represents the expectations placed upon the men of the family, preparing for university while trying to balance his sibling relationships.

Lula is Calpurnia's best friend who naturally excels at the traditional domestic skills expected of young women. She enjoys reading romance novels and practicing needlework, making her an ideal representative of the societal standards that Calpurnia actively avoids. She remains oblivious to the romantic attention she receives from several of Calpurnia's older brothers.

Viola is the dedicated cook for the Tate family who manages the demanding task of keeping the household fed. Living in a separate building on the property, she enforces household rules and tries to help Calpurnia understand her mother's strict expectations regarding social reputation. As an African American woman living in the post-Civil War South, she acutely understands the rigid social boundaries of their community.

Mr. Tate is the patriarch of the family who manages the agricultural business and the large cotton harvests. He oversees the boys' work during the harvest season and occasionally dismisses his daughter's unconventional interests, though he sometimes yields to her demands for equal treatment. He works alongside the other major landholders in Caldwell County to dictate the local agricultural schedule.

Travis is one of Calpurnia's younger brothers who possesses a deep affection for animals. He raises kittens and takes on the emotional burden of caring for the family's turkeys, showing a highly sensitive nature compared to his older siblings.

Lamar is one of Calpurnia's older brothers who adheres strictly to traditional gender expectations. He outwardly declares that girls should not earn money and frequently competes aggressively for the attention of Calpurnia's best friend.

Sam Houston is another of Calpurnia's older brothers who participates heavily in the daily operations of the family's land. He harbors a quiet affection for Calpurnia's best friend, adding to the sibling rivalry over her attention.

J. B. is the youngest brother in the Tate family. He demonstrates a sweet and observant nature, offering quiet comfort to Calpurnia when she feels overwhelmed by her mother's demands. He admits that he finds their grandfather frightening.

Sul Ross is Calpurnia's seven-year-old brother who eagerly seeks to participate in the family's work during the cotton harvest. He takes over Calpurnia's job for two pennies and waits for his turn to care for the household turkeys.

Jim Bowie is one of Calpurnia's brothers who often acts as a messenger within the large house. He helps keep track of the household moods and warns his siblings when they are in trouble with their parents.

Miss Minerva is a twenty-three-year-old woman visiting from Austin who briefly captures Harry's attention. As a member of the Independent Church, her presence causes tension within the traditional Tate household before she abruptly returns home.

Fern is a young debutante from Lockhart who stays with her cousins in Fentress. Having recently formally entered society, she represents the sophisticated social world that Harry wishes to join and quickly captures his romantic attention.

Petey is a local caterpillar collected by Calpurnia for scientific observation. Kept in a jar in her room, his unexpected transformation into a moth rather than a butterfly severely challenges her mother's aesthetic expectations for nature.