The novel follows fourteen-year-old Gina Vitay, the only child of a high-ranking Hungarian military general, during the final years of World War II. Gina's sheltered world collapses when her father dismisses Marcelle, the French governess who raised her for twelve years, because Hungary and France are on opposing sides. The General announces he is sending Gina to a boarding school in the distant city of Árkod, forbidding her from telling anyone. He refuses to explain why. Gina concludes that her father plans to remarry, but when she confronts him, his genuine astonishment destroys the theory. She mourns the loss of her familiar world: her friends, her home, and Lieutenant Feri Kuncz, a young officer she met at her aunt's afternoon teas.
The General drives Gina east across the Great Plain to the Bishop Matula Academy, a centuries-old converted monastery with iron-barred windows. At a stop along the way, he buys her a silver moon pendant; she buys him a silver ashtray, both gifts charged with unspoken grief. At the school, the stern director, Gedeon Torma, processes her enrollment without warmth. Her assigned class prefect, a young deaconess named Susanna, immediately confiscates the pendant. Gina is issued a shapeless black uniform, her hair is cut into regulation plaits, and all personal belongings are replaced with school-issue items. She hides her last treasures, including a photo album and purse, behind a metal shield in the washroom.
Classmates Mari Kis, a sharp girl on a bursary, and Piroska Torma, the director's orphaned niece, introduce Gina to the school's traditions. These include a game in which each girl is "married" to an item from the class inventory, a custom dating back to a former pupil named Mitsi Horn. They also show her a neoclassical garden statue called Abigail: If you leave a message in the statue's stone pitcher when in serious trouble, help mysteriously arrives. Gina dismisses Abigail as childish superstition.
During the annual marriage ceremony, Gina is assigned the empty aquarium as her "husband." Furious, she refuses to participate and insults her classmate Szabó. When the director interrogates her, Gina reveals the marriage tradition, a secret kept from teachers since 1914. Mari Kis saves the class by claiming the game was a one-time joke. All four girls are confined to school grounds for two weeks, but the class imposes a far worse punishment: total social ostracism. They refuse to speak to Gina and act as though she does not exist.
Susanna warns that pupils may not voice complaints to parents in letters or phone calls. Gina takes her father's Saturday call flanked by the prefect and director, forced to lie that she is happy. When her father sends homemade pastries, the class burns every one. Gina resolves to run away during Mitsi Horn's monthly tea party near the railway station, adopting model behavior so no one suspects her plan.
At the party, Gina feigns illness, climbs out a basement window, and runs to the station. On the platform she collides with König, the mild-mannered Latin teacher, who seizes her and lies to Susanna that Gina merely wandered off. Gina develops a genuine throat inflammation. She tells Susanna to check under her mattress for a farewell letter, but the prefect finds nothing there.
When her father visits, Gina pours out everything. The General reveals that he is part of an underground military resistance seeking to end Hungary's alliance with Germany. If captured, his enemies will torture Gina in his presence to force him to betray his colleagues. The Matula is the only safe place. He adds that one person in Árkod, the leader of the civilian resistance, has been entrusted with her care, someone Gina already knows. Gina swears to stay.
That night, Gina finds her farewell letter and hidden treasures returned under her mattress, along with a note signed "ABIGAIL" urging her to make peace with her class. Abigail is not a superstition but a real person operating within the Matula. Transformed by her father's revelations, Gina sees the fortress as a refuge. During a nighttime air-raid practice, as the girls huddle in a cellar holding hands with a gap around Gina, fear strips away pretenses. Gina begs forgiveness and asks to accept the aquarium as her husband. Mari Kis embraces her, and the entire class reconciles.
The weeks that follow become the happiest of Gina's life. She notices that Susanna's feelings lie not with the handsome class tutor, Péter Kalmár, but with the bumbling König. Gina writes a satirical caricature of König that a visiting Bishop accidentally reads aloud; König saves the class by claiming he assigned it. The General visits in late November, warning he may be unable to contact her for weeks. The director's aquarium is found smashed one morning. Gina later discovers forged baptismal certificates in her gym bag with an Abigail note: The aquarium was broken as cover for stealing documents. Four students are endangered by Hungary's anti-Jewish laws, and the replacement papers list their families as Reformed Protestants. Gina delivers them.
The General calls at Christmas to say he cannot visit; afterward his calls cease entirely. Months pass without contact. On March 19, 1944, Germany occupies Hungary. A week later, Gina spots Feri Kuncz in the church gallery. Through a swapped hymn book, he claims the General is ill and asks her to meet at midnight at the garden gate. Convinced Feri is the dissident her father mentioned, Gina slips out with help from friends. On the second night, as Feri tries the gate, Mráz, the glazier's assistant, catches him and rings the alarm. In her bed, Gina finds the silver ashtray she bought her father, with a note from Abigail: The General was arrested during the invasion, and Feri is an agent sent to use Gina as a hostage.
The next morning, Kuncz arrives in uniform with military orders to take Gina. Gedeon Torma refuses, citing the General's explicit instructions that she never be released to anyone, even for his funeral. When Kuncz threatens consequences, the director stands firm, declaring his superiors are the Bishop, the Church, and Christ the Redeemer.
On March 29, the director's name day, Mitsi Horn arrives and transforms the school refectory into a party. During a dance, she whispers Gina's escape plan: Kuncz will soon force the Bishop to open the school, and if Gina is found, the director will be arrested. Gina dons Susanna's clothes, passes through the unlocked gate, and civilian guides relay her through the dark streets to Mitsi's house, where Mráz gives her new identity papers as Anna Makó.
That night, Susanna arrives at Mitsi's house, having found Gina's discarded uniform. König also arrives with his own key. When soldiers search the house for a dissident, Susanna lies to protect everyone. König then reveals the truth: In his first year as a teacher, the young König brought to life the fictional miracle worker that the teenage Mitsi had dreamed up, answering pleas left in the statue's pitcher. Over decades, Abigail's work expanded to forging documents, distributing anti-war propaganda, and protecting people endangered by the state. König himself is Abigail; Mitsi was his partner. Watching from behind a door, Gina grasps the devastating irony: The person she mocked, despised, and caricatured as cowardly and ridiculous is the bravest person she has ever known, her father's colleague, and the one who saved her life.