Nina is a 29-year-old independent bookseller living in Larchmont who manages her anxiety through strict daily schedules and a rich imagination. Raised by a nanny while her photographer mother traveled, she prefers her cat and her extensive book collection over unpredictable social situations. Her carefully ordered existence faces upheaval when she learns about the massive extended family of the father she never knew.

Tom is a tall, relaxed carpenter in his early thirties with a slightly broken nose and an easygoing demeanor. As the captain of a rival trivia team, his sports knowledge and casual nature contrast directly with Nina's highly scheduled lifestyle. He believes in serendipity rather than strict planning and finds himself drawn to Nina's quick wit.

Peter is an anthropology professor and Nina's nephew. He describes himself as Nina's fabulous gay nephew and shares her dark red hair, along with her deep appreciation for office supplies. He acts as a welcoming guide, helping Nina understand the sprawling family she has just inherited.

Archie is Nina's brother, born to William's second wife around the same time Nina was born to Candice. He shares Nina's physical features and her underlying struggles with anxiety. Despite the shock of learning about his father's affair, he makes an earnest effort to welcome Nina into his life.

William is an entertainment lawyer who recently passed away, leaving behind three wives, a massive extended family, and a complex legacy. Though he was entirely absent from Nina's life, his death forces her to confront her genetic ties to him. He was an avid reader who struggled with anxiety, often running away from his problems.

Candice is an accomplished news photographer who travels the world for her career. She raised Nina as a single mother, frequently relying on a nanny due to her demanding work schedule. She holds firm boundaries regarding Nina's father, having cut ties with him decades ago after learning he was already married.

Lydia is Nina's niece, though she is chronologically older than Nina due to the wide age gap in William Reynolds's marriages. Highly intelligent and combative, she actively dislikes interacting with most people. She views Nina's sudden appearance in the estate proceedings with intense suspicion.

Liz is the owner of Knight's, the independent Larchmont bookstore where Nina works. She is passionate about literature but struggles significantly with the financial realities of running a small business. She frequently hides from the landlord to avoid conversations about her months of unpaid rent.

Polly is an aspiring actress and a millennial bookseller who works with Nina. Unlike Nina, she embraces unpredictability and often encourages her coworker to be less rigid in her routines. She uses her internet research skills to uncover details about people's private lives.

Millie is Nina's 10-year-old half-sister from William's third marriage. She is deeply attached to books and possesses a shy demeanor that makes it difficult for her to connect with children her own age. Her quiet, observant nature strongly reminds Nina of her own childhood.

Eliza is William Reynolds's third wife and widow. She provides a sense of stability for her young daughter, Millie, and offers insight into William's later years. She recognizes the introverted tendencies in her husband's family line and offers gentle advice about managing personal energy.

Becky is William Reynolds's eldest child and Peter's mother. She works as a veterinarian and holds a realistic, somewhat critical view of her father's parenting skills. She observes that William liked the concept of fatherhood far more than the actual work involved.

Lili is a widowed mother whose daughters attend Nina's elementary book club. She is currently dating a new boyfriend and dealing with the stress of preparing party favors for her sister's upcoming wedding, a task that prompts Nina to offer her assistance.

Richard is Tom's older brother and close confidant. As he prepares for his upcoming wedding to his fiancée Rachel, he offers Tom practical advice about dating, warning him to be cautious based on past relationship experiences.

Phil is Nina's pet cat and primary roommate. He serves as an anchor in Nina's highly structured life, offering her companionship and a sounding board for her active imagination without the pressure of human interaction.