Perempuán awakens inside a brutal, vertical prison that stretches to 333 floors, with one cell per level and two inmates sharing each space, all centered around a hollow shaft. A platform laden with food descends this shaft daily, pausing at every floor for only two minutes. Those on higher levels get first access to the meals, while inmates on lower floors risk starvation as the platform passes. Before entering, every prisoner is interviewed and selects a daily dish that will be provided each day on their level, and each inmate is allowed to bring one personal item. At the end of each month, prisoners are randomly reassigned to new floors, keeping everyone guessing about who will be their neighbor next.
On level 24, Perempuán shares a cell with a large man named Zamiatin, named after Yevgeny Zamyatin. A Loyalist from the level above, Robespierre, explains the informal system that currently governs the prison. Two factions exist: Loyalists, who follow strict, self-imposed rules about eating only their chosen food (or trading only by consent), and Barbarians, who eat whatever they can grab. Robespierre argues that the Loyalist law ensures a fairer distribution of the food.
Tensions flare quickly when inmates from higher levels eat food meant for others, triggering violence, deaths, and injuries. Perempuán and Robespierre work to defend their level and keep order, while they learn about The Messiah, a mythical figure who is said to have survived a month without food through meditation and who sacrificed his own leg to feed others on the lowest levels. His followers, the Anointed Ones, spread his message of the Loyalist laws.
As days pass, Zamiatin and Perempuán grow closer, sharing food and personal stories. It is revealed that Perempuán entered the prison grieving after accidentally causing the death of her then-boyfriend’s son, while Zamiatin is a disillusioned mathematician. Zamiatin, in violation of the law, sometimes eats a portion of food from prisoners who have already died. Word of this spreads, and to protect Perempuán from punishment, the already ill Zamiatin sets himself on fire and leaps into the pit.
The following month, Perempuán is paired with Sahabat on level 51. They ride the platform down to punish two Barbarians who have eaten others’ food. In conversation with Sahabat that night, Perempuán learns of a particularly brutal Anointed One, Dagin Babi, who methodically kills both Barbarians and Loyalists who commit minor infractions. Sahabat plots to fake their deaths by consuming portions of an oil painting at a lower level, which contains a substance that will render them immune to the knockout gas used at the end of each month, with the aim of being disposed of outside the facility. When Dagin and his followers arrive to punish disobedience, they kill Sahabat and cut off one of Perempuán’s arms.
The next month, Perempuán awakens on level 72 with Trimagasi, Zorion Eguileor. Disillusioned with Loyalist ideals, she recruits a group of Barbarians, ostensibly to challenge the Loyalists but truly to find the painting. A bloody battle ensues, and Perempuán and Trimagasi emerge as the sole survivors.
Perempuán eventually locates the painting and consumes a portion of it. She passes out and later awakens on level 333, bundled among corpses being disposed of. Gravity seems suspended as workers in gas masks reset the prison. She spots a young boy and, choosing to save him, forgoes escape. She encounters other prisoners living on the lower level, implied to be a purgatory for dead souls, who urge her to return the boy to the upper levels while she remains below with them. In a poignant twist, Perempuán reunites with Goreng, Ivan Massagué, who is presumably her ex-boyfriend.
