Polly is a 40-year-old English teacher at an all-girls private academy in Manhattan. She is dealing with years of infertility, her father's progressing dementia, and a complicated relationship with her emotionally distant mother. When she takes the ancestry test, the experience prompts an existential journey into her personal history and her understanding of family.

Sarah is Polly's closest friend and a fellow member of their unique book club. A generous, kind, and unpretentious breast cancer survivor, she provides a steady anchor for Polly through her fertility struggles. She is married to Richard and acts as a stepmother to his sons, showing deep care for the people in her community.

Mark is Polly’s second husband and a large-animal veterinarian at the Bronx Zoo. He is a kind, steady, and deeply attentive partner who supports Polly through their shared fertility struggles. He remains a calm and grounding presence as Polly questions her identity and family history.

Josephine is a sharp, outspoken, and intellectually confident student in Polly's English class. Bound for Harvard, she struggles under the intense weight of her wealthy parents' academic expectations and looks to Polly as a mentor and maternal figure.

Helen is a reliable member of Polly's tightly knit book club. Having experienced early menopause, she offers empathetic support to Polly as they face the unpredictability of womanhood and aging together.

Jamie is a loyal member of Polly's monthly book club, a group that values honest connection over actual literary discussion. She occasionally seeks advice from the group regarding her community involvement and personal life.

Garrison is Polly's brother, serving as a stabilizing, if sometimes sarcastic, force in her life. Confident in his understanding of their family history, he encourages his sister to let go of her resentments while remaining a protective confidant.

Jack is Polly and Garrison's father. Residing at the Edgemere nursing facility, he is experiencing progressive dementia. He has always been a primary source of love and stability for Polly, making his cognitive decline especially painful for her to witness.

Mary is Polly and Garrison's mother, a highly accomplished and pragmatic judge. Her relationship with Polly has always been emotionally distant and complicated, a dynamic that comes under further strain as Polly asks new questions about the family's past.

Talia is a 16-year-old girl from Bennington, Vermont. Grieving the recent loss of her mother, she begins searching for historical family connections, leading her to initiate a correspondence with Polly.

Stephen is Talia’s father, a man who travels frequently for work. He meets with Polly to discuss his daughter's recent outreach, leading to a conversation that raises new questions for Polly regarding her own background.

Barbara is Stephen’s mother and Talia’s grandmother. She runs Earthshine, an alpaca farm in the Catskills, and possesses a perceptive, somewhat mystical demeanor that leaves a strong impression on Polly and her friends.

Andre is a carpenter and Barbara Burton's partner. He lives and works at the Earthshine alpaca farm, maintaining a detached demeanor and holding firm beliefs that genetics matter far less than lived experiences.

Jeannine is the psychologist at Polly’s fertility clinic. She provides a rare, judgment-free clinical space where Polly feels safe to share her deepest fears, secrets, and frustrations regarding her inability to conceive.

Lou is Mark’s mother and Polly’s mother-in-law. Warm, nurturing, and deeply devoted to her large family, she represents the quintessential maternal figure in Polly’s life, offering the emotional comfort Polly misses from her own mother.

Skipper is Mark's father and the patriarch of their close-knit family. He enjoys a bustling household and shares a strong, supportive bond with his wife, Lou, and their children.

Emily is Mark’s sister and a professional psychologist. Having faced her own familial challenges, she offers Polly realistic advice about the complexities of biology and family dynamics.

Claire is a resident at the Edgemere nursing facility who forms a companionship with Jack, offering him quiet connection as his dementia progresses.

Constance, known as "CC," is a notorious student in Polly’s English class. Her disruptive behavior and shallow remarks mask a difficult home life involving a stepmother and an absent biological mother, testing Polly's patience and empathy in the classroom.

Carrie is Josephine's mother. Despite her husband's rigid academic expectations for their daughter, Carrie recognizes the positive influence Polly has on Josephine and encourages their continued mentorship.

Richard is Sarah's late husband. He married Sarah later in life and brought his two sons into the marriage, helping form the family structure that Sarah deeply cherishes.

Carter is Sarah's stepson. He meets with Polly to handle estate affairs and ensure his stepmother's final wishes are respected regarding the cottage and her belongings.