Matthew is a 13-year-old boy living in Leonia, New Jersey, adjusting to the 2020 COVID-19 lockdown. Stuck at home taking online classes, he feels isolated from his friends and misses his father, who is stranded overseas. When his mother assigns him the chore of helping his great-grandmother sort through her belongings, he uncovers letters and photographs that prompt him to ask questions about his family history. Through his journaling and research, he begins piecing together his ancestors' experiences.

Mila is a 12-year-old girl living a comfortable life in 1932 Kyiv, Ukraine. As a dedicated member of the Young Pioneers, she respects Soviet leadership and trusts her father completely. Her mother died in childbirth, leaving Mila wholly reliant on her father and their housekeeper for stability. When a starving girl arrives at her door claiming to be family, Mila initially rejects the information because it contradicts everything she has been taught about her country and her father's past.

Helen is a 12-year-old girl living in Brooklyn, New York, during the Great Depression. She frequently clashes with her father over food, unaware at first of his intense anxiety regarding his starving relatives in Ukraine. She desperately wants to fit in at school and hide her cultural differences from her classmates. Learning about the Ukrainian famine prompts her to collect local stories and write to newspapers in an attempt to help her overseas family.

Nadiya is a young girl who arrives starving at Mila's doorstep in Kyiv. She identifies herself as the daughter of Mykola Lomachenko, making her Mila's cousin. She explains that her family was forced onto a collective farm, where they suffered starvation and loss after the government confiscated their resources. Despite her traumatic experiences and severe malnutrition, she maintains a determined spirit and seeks help from her estranged uncle.

GG is Matthew's 100-year-old great-grandmother. Following the outbreak of the COVID-19 pandemic, her family moves her from a nursing home into their New Jersey house to keep her safe. She initially refuses to discuss her past or open the boxes containing her vinyl records, old photographs, and documents. Eventually, she agrees to share her memories of growing up in Ukraine during the 1930s with Matthew.

Matthew's father is a journalist stranded in Paris due to international border closures during the COVID-19 lockdown. He frequently communicates with Matthew over the phone, offering advice on coping with the lockdown. He encourages Matthew to document his life during the pandemic by sending him a red notebook and giving him tips on interviewing subjects.

Mom is Matthew's mother, who works as a magazine editor from their home in New Jersey. She balances her job with managing Matthew's online schooling and enforcing strict lockdown rules to protect her elderly grandmother, GG, from the virus. Her protective measures frequently cause friction with Matthew, who feels stifled by the isolation.

Lev is Mila's father and an influential member of the communist party in Kyiv. He provides a luxurious life for his daughter, complete with private piano lessons and specialty chocolates, while shielding her from the harsh realities outside their home. He claims to be an orphan with no living relatives, a story that is challenged when his niece Nadiya arrives seeking help.

Vanya, often called Pop, is Helen and Peter's father, living in Brooklyn. He immigrated to the United States from Ukraine and suffers severe anxiety over the fate of his brothers and their families still living in the Soviet Union. His rigid enforcement of eating every scrap of food stems from his knowledge of the famine, a fact that becomes clear after he suffers a heart attack.

Mama is Helen and Peter's Russian mother. When her husband suffers a heart attack and cannot work, she takes on extra cleaning jobs and accepts help from neighbors to support the family. She acts as a mediator between her husband's strict rules and her daughter's desire to fit in as an American.

Anna is Mila's private piano teacher in Kyiv. She holds different political views from Mila's father but maintains a professional and kind demeanor during lessons. When Mila brings a starving Nadiya to her door, Anna risks her own safety and possible arrest by the secret police to provide the girl with temporary shelter.

Ruth is Helen's Jewish classmate in Brooklyn. When their teacher dismisses the reports of the Ukrainian famine, Ruth approaches Helen to share that her own community has heard similar stories. She encourages Helen to draft a letter to the New York Times and helps her edit it, showing Helen that it is acceptable to be proud of her heritage.

Katya is Mila's best friend and a fellow member of the Young Pioneers in Kyiv. Together, they form the Committee of the Motherless Daughters of the Communist Party, since both lost their mothers. Mila increasingly distances herself from Katya to keep Nadiya's existence a secret.

Dasha is the housekeeper for Mila and Lev Lomachenko. She manages the daily household chores and frequently fusses over Mila's safety and health. She survived a typhus outbreak during the war and maintains a cautious, quiet presence in the home.

Mykola is Nadiya's father and the brother of Lev and Vanya. After resisting the state's agricultural policies, he is arrested and sent to Siberia. His absence leaves his family vulnerable to the ensuing starvation on the collective farm.

Peter is Helen's younger brother. He lives with his family in Brooklyn and occasionally faces bullying in the neighborhood, prompting Helen to fiercely protect him.

Olga is Anna Mikhailovna's mother. She lives with her daughter in Kyiv and helps care for Nadiya when Mila brings her to their home for refuge.

Josh is one of Matthew's friends from school. Because of the lockdown rules enforced by Matthew's mother, Josh can only interact with Matthew through text messages or by waving from a distance through the window.