The Devil's Arithmetic recap

Hannah Stern, a modern Jewish girl tired of hearing about the Holocaust, opens the door for Elijah during a Passover Seder and finds herself in a Polish village in 1942. Known there as Chaya, she joins relatives preparing for Shmuel and Fayge's wedding. Nazis interrupt the celebration and deport the villagers to a concentration camp. Hannah's knowledge of history cannot prevent their suffering, but she learns the camp's rules from a prisoner named Rivka and helps preserve memory by telling stories and caring for others. Shmuel and Fayge are killed after an escape attempt, while Yitzchak gets away. When Rivka is selected for death, Hannah takes her place and is sent to a gas chamber. She returns to the Seder at the instant she left. Hannah then recognizes Aunt Eva as Rivka and Grandpa Will as Rivka's brother Wolfe. Aunt Eva explains that Chaya died to save her and that Hannah bears Chaya's name, giving Hannah a new understanding of sacrifice and remembrance.

Hannah Stern travels with her parents and younger brother Aaron to a family Passover Seder. She is frustrated by the rituals and by older relatives who return repeatedly to memories of the Holocaust. Grandpa Will, a survivor with a number tattooed on his arm, becomes distressed by televised images of Nazi persecution; Aunt Eva calms him and treats Hannah's impatience with sympathy. During the Seder Hannah is asked to open the apartment door symbolically for the prophet Elijah. When she does, the hallway has vanished. Outside is open countryside, and a woman in old-fashioned clothing calls her by the name Chaya. The woman behaves as though Hannah is a recently orphaned relative expected to be part of a family wedding in a Polish village.

Hannah finds herself treated as Chaya, the niece of Gitl and Shmuel, whose parents have recently died. No one understands her references to modern New York, and her memories of her own life begin to feel less secure. Gitl prepares the household for Shmuel's marriage to Fayge. Hannah meets villagers including the widower Yitzchak and his young children, and she shares modern stories with girls who accept her as a new friend. She recognizes that the date is 1942 and tries to warn the others about the Nazis, but her alarm sounds like confused illness or fantasy to people focused on the wedding. The party travels to Fayge's village, where music, ceremony, and communal celebration briefly surround Shmuel and his bride.

Nazi soldiers interrupt the wedding gathering and announce that the Jews are being relocated. Hannah understands the threat and urges resistance, but the armed soldiers control the village and the adults cannot accept the full scale of what she predicts. The villagers are crowded into sealed railway cars with almost no air, water, or room to move. During the journey, terror, thirst, and exhaustion replace the wedding celebration; some prisoners die before the doors open. At the camp, shouted orders and violence strip away any remaining belief that cooperation will keep families safe. Men and women are separated, possessions are taken, and the prisoners are forced toward processing and selection. Hannah's foreknowledge tells her where these steps lead, but it gives her no power to stop them.

The women are shorn, given rough clothing, tattooed with numbers, and absorbed into the camp's brutal routines. Young children and prisoners judged unable to work are taken away; smoke and ash make their fate clear. Hannah struggles to hold on to both her present identity and the fading memory of her life as Hannah. A more experienced prisoner named Rivka teaches the newcomers practical rules: save food, conserve strength, learn what each guard and work detail expects, and look after one another without drawing notice. Rivka and her younger brother Wolfe demonstrate how fragile survival is and how much it depends on shared knowledge. Gitl, Fayge, and the other women try to remain connected even as the camp reduces them to numbers and labour.

Time in the camp is measured by roll calls, hunger, work, selections, and sudden death. Hannah grows thinner and less certain of the modern future she once knew. Rivka's rules help the prisoners avoid some dangers, while Gitl's determination helps hold their small group together. Hannah contributes by telling stories, giving the others a temporary mental refuge and preserving names and lives in memory. Losses continue, including children and friends who cannot survive the camp's violence and deprivation. The inmates learn that remaining human requires small acts of attention and solidarity even when those acts cannot guarantee survival. Hannah's earlier boredom with remembrance has been replaced by an understanding that remembering a person is itself a form of resistance to a system designed to erase them.

Shmuel, Yitzchak, Gitl, and others take part in an escape attempt. The plan is discovered before most can get free, although Yitzchak escapes. Shmuel and the captured prisoners face execution. Fayge breaks from the women to join Shmuel, and the two die together. Gitl survives but is devastated by the loss of her brother. Soon afterward guards choose another group of women for the gas chambers, including Rivka. Hannah understands that Rivka is meant to live into the future Hannah remembers. She takes Rivka's place and tells her to run. Walking toward death with the other women, Hannah holds to the knowledge that sacrifice can save a life and carry memory forward. As the gas-chamber door closes, the camp disappears from her awareness.

Hannah finds herself back at the Seder at the instant she opened the apartment door for Elijah. Her family believes no time has passed, but Hannah now recognizes people and details from the camp. She identifies the number on Aunt Eva's arm as Rivka's and understands that Grandpa Will is Rivka's brother Wolfe. Aunt Eva confirms that she was once the girl Hannah knew. She explains that Yitzchak escaped and fought with partisans, that Gitl survived, and that Wolfe also lived, though many others did not. Most importantly, Aunt Eva remembers Chaya as the girl who exchanged places with her and died so that she could escape selection. Hannah learns that she was named for Chaya. The family stories that once seemed repetitive now connect her directly to the people whose choices made her life possible, and she joins the Seder with a new commitment to remember them.

When guards seize Rivka for a group being sent to the gas chambers, Hannah exchanges places with her and urges Rivka to run. Hannah enters the chamber remembering that each saved life matters and that her own sacrifice may preserve the future she knows. She is suddenly back at her family's Seder, standing at the apartment door after opening it for Elijah. The experience has changed her understanding of remembrance. Hannah recognizes Aunt Eva's tattoo as Rivka's number and identifies Grandpa Will as Rivka's brother Wolfe. Aunt Eva confirms their past and explains what became of several people Hannah knew: she and Wolfe survived, Gitl also survived, and Yitzchak escaped and fought the Nazis, although his children were killed. Aunt Eva reveals that the girl called Chaya died saving her, and that Hannah was named for that girl. Hannah can now receive the survivors' stories as personal memories and acts of preservation rather than as an unwanted family ritual.