The Narrator is the youngest of the 40 female prisoners and the only one who entered captivity as a young child. Lacking memories of the outside world, she possesses an intense, unfiltered curiosity about her surroundings and her own mind. Because the older women withhold information about life before their imprisonment, she feels emotionally disconnected from them. She seeks mental stimulation by theorizing about their jailers and secretly counting her heartbeats to track time.

Anthea is a former nurse and the most educated woman among the prisoners. She acts as a maternal figure to The Narrator, answering questions about anatomy, time, and human reproduction when the others refuse. She retains a strong desire to preserve her medical knowledge, even though it serves little practical purpose in their confined existence. Her kindness and willingness to communicate help integrate the young girl into the broader group.

Dorothy is the eldest and most respected woman among the captives. Despite physical frailty and a weak heart, she possesses a stubborn determination and natural leadership abilities. She organizes the women, plans their routines, and insists on pushing forward to find answers about their captivity rather than settling into complacency.

The Guards are the silent, male enforcers who oversee the underground bunker. Armed with whips, they enforce strict rules against touching, communication, and emotional expression. They never speak, leaving the prisoners completely ignorant of their motives, origins, or the broader power structure they represent.

The Women represent the 39 adult prisoners who share the underground bunker with The Narrator. Having lived ordinary lives before their abrupt incarceration, they miss the societal structures, romantic relationships, and basic comforts they once knew. As a collective, they struggle to adapt to sudden freedom, preferring familiar routines over the terrifying uncertainty of their new environment.

Frances is a fellow prisoner who sleeps beside The Narrator in the underground bunker. She understands the strict rules of their captivity and warns the young girl about the consequences of drawing the captors' attention. She represents the basic human comfort that the youngest prisoner instinctively craves but is forbidden to seek.

Rose is one of the adult women imprisoned in the bunker. She brings a rare moment of beauty and emotional release to the group by singing aloud. Her voice provides The Narrator with her very first experience of music, triggering a profound physical and emotional response in the young girl.

Mary-Jane is one of the adult prisoners who survives the initial confinement. She struggles with the harsh realities of their mysterious environment and suffers from severe stomach ailments. Her rapid physical deterioration deeply affects the group's morale and their willingness to keep moving forward.

Angela is a prisoner who falls gravely ill after the group escapes. Facing immense physical suffering, she desires an end to her pain and looks to the medically trained members of the group for relief. Her condition forces the group to confront difficult moral choices regarding mercy and survival.

Anna is one of the women who survives the escape but later experiences severe health decline. Her partial paralysis renders her dependent on the others in a world completely lacking in modern medical facilities. She actively seeks relief from her agonizing physical condition.

Laura is one of the original adult prisoners. Unlike the fiercely curious young protagonist, Laura shows little interest in exploring their unfamiliar world or understanding their circumstances. Despite having a relatively healthy body, she lacks the internal drive to adapt to her new reality, remaining tethered to the memory of a past that no longer exists.