Mirielle is a wealthy 1920s Los Angeles socialite and the wife of a prominent silent film star. Following a diagnosis of Hansen's disease, she is forcibly separated from her luxurious life and quarantined at a facility in Carville, Louisiana. Accustomed to deference and high-society comforts, she initially responds to her confinement with fierce denial and views the other patients as socially inferior. Her desperation to return to her children drives her early decisions at the colony.

Sister Verena serves as the no-nonsense head nurse at the Carville facility. She expects strict adherence to the colony's rules and refuses to grant special treatment to anyone, regardless of their outside wealth. She assigns daily tasks and oversees medical care with a highly disciplined approach, demanding that patients contribute to the community.

Frank is a World War I veteran and Louisiana native who has resided at Carville for an extended period. Hansen's disease has visibly affected his hands, a physical reality that unsettles newcomers. Despite his confinement, he remains highly active in the community as a leader in the What Cheer Club, organizing social events to boost morale.

Irene is a patient and the head orderly of house 18, the residence where Mirielle is assigned. Hailing from a farming background in Texas, she is a talkative and pragmatic woman who approaches her condition without shame. She values hard work and frequently challenges Mirielle's sense of superiority.

Jean is a nine-year-old girl who lives at Carville. Abandoned by her family at the colony, she responds to her isolation by refusing to speak and skipping school. She regularly pulls pranks on the adult residents, seeking attention through mischievous behavior rather than conversation.

Hector is a Mexican agricultural worker who shares the arduous train journey from California to Carville with Mirielle. He experiences heavy discrimination and ethnic slurs but handles the abuse with quiet dignity. He works hard at the facility to send money back to the family that ostracized him.

Charlie is a successful silent film actor and Mirielle's husband. Deeply invested in his career and public image, he chooses to maintain physical and emotional distance from Mirielle after her diagnosis. He manages their household in California and controls the narrative about his wife's disappearance for the Hollywood press.

Evie is Mirielle and Charlie's older daughter. She remains in Los Angeles under the supervision of a nanny while her mother is quarantined in Louisiana.

Helen is Mirielle's young daughter, living in the family's California home. She is too young to fully comprehend her mother's sudden disappearance.

Felix is Mirielle and Charlie's deceased son. He accidentally drowned in a pool prior to the events of the novel, leaving an enormous psychological impact on his parents and fracturing their marriage.

Dr. Jachimowski, known informally as Doc Jack, is a physician at the Carville facility. He conducts thorough skin examinations, takes tissue samples, and delivers direct medical assessments to the quarantined patients.

Dr. Ross is the Medical Officer-in-Charge at Carville. He oversees the administrative and medical protocols of the colony, pushing patients to take jobs to integrate into the community and find purpose during their confinement.

Samuel is a resident at Carville who previously spent a decade running from authorities to avoid being quarantined. He speaks openly about the facility's perimeter fence and jail, sparking Mirielle's early thoughts of escape.

Sister Beatrice is the pharmacist at Carville. She oversees the preparation of chaulmoogra oil capsules, experimenting with additives like cocoa powder to make the treatments less nauseating for the patients.

Madge has lived at the quarantine colony for twenty-one years. Confined to house 18, she frequently asks for assistance and attention, taking immense joy in simple luxuries like having her hair styled and wearing makeup.

Sister Loretta is a nurse at Carville who guides new workers through their medical rotations. She attempts to ease Mirielle's fears about the disease by explaining standard sanitation practices.