Zofia is a seventeen-year-old high school senior living in Warsaw. She possesses a deep love for literature and aspires to write, frequently seeking refuge in the pages of banned books. As the Nazi occupation alters her city, she transitions from a student to a full-time library worker. Her anger toward the occupation drives her to find ways to resist, specifically by protecting the library's collection and distributing books to marginalized citizens.

Janina is a warm, outgoing Jewish high school senior who dreams of becoming a teacher. She frequently acts as a balancing force for Zofia's more reserved personality. As antisemitic decrees restrict her freedom, Janina adapts by organizing small educational and reading groups for children. Her natural empathy is severely tested by the worsening conditions she and her family face in the city.

Matka is Zofia's practical and composed mother. She maintains a formal household, enforcing strict boundaries that initially create emotional distance between her and her daughter. Her background as a nurse gives her a pragmatic approach to emergencies. When the war separates her from her husband and son, she struggles with despair before ultimately focusing her energy on protecting Zofia.

Darek is a confident young artist and the nephew of a local librarian. He frequently sketches and paints scenes of Warsaw, capturing the city's changing environment. His relaxed charm masks a deep involvement in the underground resistance. He acts as a crucial link for Zofia, helping her safely communicate with others and encouraging her to channel her anger into organized, careful rebellion.

Antek is Zofia's older brother. He possesses a strong sense of duty to his country and actively follows the escalating military tensions. Driven by patriotism, he leaves his family in the cover of darkness to join the armed forces defending the city shortly after the bombings begin.

Dr. Nowak is Zofia's father and a dedicated physician. He treats wounded civilians and soldiers during the height of the bombings. He values literature and critical thinking, secretly hiding his personal book collection under the floorboards of his study to prevent confiscation. He encourages Zofia's rebellious spirit and maintains secret correspondence with other medical professionals regarding infectious diseases.

Danuta is a young woman studying to become a librarian alongside her friend Kasia. She is slightly older than Zofia and shares the group's passion for forbidden literature. She actively secures library jobs for Zofia and Janina after they are expelled from school.

Kasia works in the children's reading room at the Warsaw library. She possesses a gentle demeanor well-suited for comforting frightened children during air raids. As the occupation intensifies, she bravely assists with the clandestine book club and helps manage the secret circulation of reading materials.

Mrs. Mazur is a seasoned warehouse librarian who takes Zofia under her wing. She recognizes the threat to Poland's cultural history and actively plots to protect the library's collection. She teaches Zofia how to manipulate the official catalogs to save banned books from destruction.

Krystyna is the captain of Zofia and Janina's Girl Guides troop. She assigns the girls to help with cleanup and rescue efforts during the initial bombings. Later, she transitions into organizing underground education, hosting secret high school classes disguised as an embroidery group.

Maria is a dedicated member of the Girl Guides and an original member of the friends' reading group. She volunteers alongside Zofia and Janina to extinguish fires and clear rubble during the heavy bombings of Warsaw.

Miss Laska is an elderly librarian with an exceptional memory for the library's entire catalog. Despite her age and failing health, she maintains a fierce dedication to her reading room and willingly risks her safety to run a covert lending operation for banned books.

Herr Nagiel is the Nazi official assigned to oversee the Warsaw library system. He implements strict rules, ordering the removal of French and English texts and establishing a reading room exclusively for Germans. He relies on literal interpretations of his own orders, which the librarians exploit.

Mrs. Steinman is Janina's mother. She attempts to keep her family safe by downplaying their Jewish identity and complying with early occupation orders. She endures forced labor and worsening conditions as her family is moved into the sealed ghetto.

Mr. Steinman is Janina's father. He attempts to provide for his family as their rights and resources are systematically stripped away. He continues to work inside the ghetto even as conditions become dire.

Marta is a famous Polish romance novelist whose work Zofia greatly admires. She offers Zofia writing advice, explaining that true emotional power in writing comes from experiencing genuine pain. She eventually uses underground presses to continue publishing during the occupation.

Veronica is the author of an underground pamphlet protesting the treatment of Jews, though her writing also contains nationalistic biases. She operates within a clandestine smuggling organization and recruits Zofia to help escort fugitives to safehouses.

Mrs. Borkowska is a neighbor in the Nowaks' new apartment building. She is highly observant of the building's comings and goings and prioritizes the collective safety of the tenants over harboring fugitives.

Mrs. Berman is a dedicated librarian who previously offered to teach Janina Yiddish. After being forced into the ghetto due to her Jewish heritage, she establishes a children's reading room disguised as a daycare to provide comfort to the children there.

Ewa is an eight-year-old girl tasked with caring for her four younger siblings while her mother works. Having left school early, she struggles with reading until Zofia takes the time to tutor her.

Dr. Weigl is a medical professional who corresponds with Dr. Nowak. He successfully procures and smuggles valuable typhus vaccines to Zofia, ensuring they reach those in desperate need.

Frau Schmidt is one of the two Nazi women assigned to take over the library's administration. She is highly observant and runs the facility with ruthless efficiency. Her sharp oversight makes it significantly harder for the local staff to conceal banned materials.

Frau Beck serves as the second half of the new German leadership at the library. Together with Frau Schmidt, she ensures that local logs are destroyed and rewritten in German, directly threatening the preservation efforts of the local staff.

Ella is a widow living in the countryside who provides a safehouse for those fleeing the city. She refuses Zofia's money for supplies, asking instead for reading materials to start a small collection for the locals.