Nineteen years old and the last of the "Blues" in Kentucky, Cussy Mary works as a Pack Horse Librarian delivering books to remote mountain families. She travels the dangerous trails to earn her own wages, resisting her father's attempts to arrange a marriage. Her blue skin makes her a target for extreme prejudice in the local town, but she finds safety and purpose in literature and her library route.

A Kentucky coal miner suffering from an occupational lung illness. He purchases items like a mattress for his daughter despite being paid in company scrip. He attempts to protect Cussy Mary by securing a marriage for her, honoring a promise made to his deceased wife. He also attends secret miners' union meetings to protest the dangerous working conditions enforced by the mining company.

A wealthy bachelor who has returned to his ancestral mountain land after spending years in the West. He requests specific, sometimes controversial, books from the library service. He treats Cussy Mary with respect, offering apples to her mule and discussing literature without demonstrating the prejudice common among the townspeople.

A local preacher and cousin to Charlie Frazier. He hunts down people with physical differences in the mountains, believing their traits are signs of sin. He waits in the woods to trap Cussy Mary, using his religious authority to justify violence and harassment against those he considers abnormal.

The wealthy village physician who operates a practice in town and conducts medical research in Lexington. He possesses resources like an automobile and employs a housekeeper. He provides occasional medical care and food to Cussy Mary, but uses blackmail to force her into acting as a test subject for his blood disorder research.

An unkempt man who seeks to marry Cussy Mary primarily to acquire her land and dowry. He evaluates her property deed during his courtship visit. Following their wedding, he attempts to force himself on her, revealing his cruel and abusive nature.

A sixteen-year-old library patron living in a remote cabin with her older husband. She practices reading and writing letters in the dirt under Cussy Mary's instruction. She completely accepts her librarian's skin color, eagerly welcoming her visits and exchanging food or seeds for reading materials.

Angeline's thirty-year-old husband. He sustains an unhealing gunshot wound during a theft and relies on his wife for care. He holds deep prejudice against Cussy Mary and resents her presence in his cabin, even when she reads to him and provides medical herbs.

A stubborn, intelligent pack mule named after a female apostle. She serves as Cussy Mary's reliable transport on the dangerous mountain trails. Having suffered abuse in the past, she is wary of men but fiercely protective of her librarian companion, frequently alerting her to danger.

A Black Pack Horse Librarian who carries a dictionary to satisfy her interest in words. She works out of the same Library Center as Cussy Mary, where they both face severe discrimination and exclusion from their white supervisors. She plans to move to Pennsylvania to work at a Free Library and attend library school.

A white librarian at the center who openly displays bigotry toward Cussy Mary and Queenie. She uses hurtful remarks, refuses to touch materials handed to her by Cussy Mary, and actively attempts to sabotage the employment of her marginalized colleagues.

The supervisor at the library center who enforces a strict racial hierarchy among the librarians. She actively upholds segregation policies, going so far as to post a discriminatory sign by the center's new bathroom to exclude Cussy Mary and Queenie.

A dedicated schoolteacher who requests books for her impoverished and malnourished students. She acts as a compassionate ally, visiting Cussy Mary after a traumatic event without asking invasive questions. She advocates for broad outreach programs to feed all her pupils rather than singling out just one.

A young, malnourished student who admires Cussy Mary and dreams of becoming a librarian himself. Despite suffering from hunger and illness, he highly values the books she brings and gifts her a precious pineapple candy won in a spelling bee.

A local moonshiner who initially opposes the library service, viewing reading as a distraction from necessary chores. He strictly controls his family's access to reading materials, but slowly accepts practical texts like home remedy guides and agricultural magazines.

A visually impaired woman who refuses government-issued books on principle but uses them to prop up furniture. She offers Cussy Mary herbal remedies and accepts her physical assistance with eye-washing chores, showing a complete lack of prejudice regarding skin color.

A young library patron aspiring to become a forest ranger. He requests forestry reading materials and relies on Cussy Mary to help deliver his courtship letters, as he faces strict opposition from his girlfriend's father.