Cussy is a woman from Kentucky with a hereditary condition called methemoglobinemia, which turns her skin blue. A former Pack Horse librarian, she is imprisoned in the Kentucky State Reformatory for Women for marrying a white man. Facing severe institutional abuse and social ostracism, she relies on her passion for books to bring comfort and literacy to her fellow inmates, transforming a neglected prison library into a functioning service.

Waldeen is a pragmatic "lifer" who runs the prison kitchen. A former brothel madam, she carries a deep-seated distrust of authority and understands societal hypocrisy. She offers Cussy quiet protection and practical advice, serving as a vital ally who shields her from the hostility of other inmates.

Mrs. Claxton is the director of the Louisville Western Colored Branch Library. A respected community leader, she dedicates her life to empowering Black citizens through literacy and voter registration. She becomes a radical agent of justice, risking her own safety and breaking the law to protect Cussy from institutional violence.

Warden Sanders is the stern, authoritative head of the Kentucky State Reformatory for Women. She views the inmates as logistical problems and strictly enforces institutional control to maintain funding. She serves as the primary enforcer of dehumanizing, state-sanctioned medical and penal policies against the prisoners.

Jackson is Cussy's white husband, imprisoned in the men's penitentiary for violating Kentucky's laws against interracial marriage. His unwavering love and support provide Cussy with her emotional anchor. He longs to return to their mountain home and hates the urban life they are eventually forced to endure.

Regina is a young, volatile inmate who initially holds the librarian position Cussy desires. Traumatized by past institutional abuse, she projects her insecurity onto Cussy and attempts to sabotage her. Her initial hostility stems from a desperate need for purpose and a deep sense of loss.

Sassyann is an inmate on Death Row, convicted of poisoning her abusive husbands. Resigned to her fate, she finds unexpected solace when Cussy teaches her to write letters to her estranged sons. She represents the devastating physical and legal impact of domestic violence.

Honey is Cussy and Jackson's sixteen-year-old adopted daughter. Left without her parents, she relies on her job at a local library and sends letters to Cussy that provide a crucial link to the outside world. She continues her mother's legacy by embracing the role of the "Book Woman."

Susan is Mrs. Claxton's niece and a nursing director in Louisville. Initially intrigued by Cussy's genetic condition, she quickly becomes a compassionate ally. She uses her medical expertise to shield Cussy from institutional harm and manages her own secret interracial relationship.

The Reverend is Mrs. Claxton's husband and a community leader in Louisville. He initially holds strict, conservative views about propriety, hesitating to associate with sex workers, but can be persuaded to support righteous causes when presented with moral arguments.

Miss Rose is Mrs. Claxton's sister and the owner of the Rose & Shine boardinghouse. She provides crucial sanctuary and employment for Cussy when the protagonist is forced into hiding.

Doc Thomas is Cussy's longtime physician from Troublesome Creek. He attempts to advocate for her well-being from the outside, though the prison administration actively works to block his interference.

Officer Holt is a guard in the women's prison. Though initially hardened by the violent environment, he comes to recognize and defend the positive impact of Cussy's library service on the inmates' mental health.

Buttermilk is a kind war veteran and inmate from the men's prison who speaks French. He helps refurbish the library space and provides Cussy with updates about her husband's well-being.

Daniel is a young inmate in the men's penitentiary who suffers physical abuse from other prisoners due to his forbidden love for another man. Cussy helps him write a letter, establishing a silent solidarity between two people criminalized for their relationships.