In a small town near Tampa, Florida, seven-year-old Mary Adler lives with uncle and de facto guardian, Frank. Her best friend is her 40-ish neighbor, Roberta. On her first day of first grade, she shows remarkable mathematical talent, which impresses her teacher, Bonnie Stevenson. There, despite her initial disdain for average children her own age and her boredom with their classwork, she begins to bond with them when she brings her one-eyed cat, Fred, for show-and-tell and later defends a classmate from a bully on the bus. Mary is offered a scholarship to a private school for gifted children. However, Frank turns it down. Based on his family’s experiences with similar schools, he fears Mary will not have a chance at a “normal” childhood.
It emerges that Mary’s mother, Diane, had been a promising mathematician, dedicated to the Navier–Stokes problem (one of the unsolved Millennium Prize Problems) before taking her own life when Mary was six months old. Mary has lived with Frank, a former college professor turned boat repairman, ever since.
Frank’s estranged mother and Mary’s maternal grandmother, Evelyn, seeks to gain custody of Mary and move her to Massachusetts, believing that Mary is a “one-in-a-billion” mathematical prodigy who should be specially tutored in preparation for a life devoted to mathematics, much as Diane was. However, Frank is adamant that his sister would want Mary to be in a normal public school and have the childhood she didn’t have. Worried that the judge will rule against him and he will lose Mary completely, Frank accepts a compromise brokered by his lawyer Greg Cullen that sees Mary placed in foster care and attend the private school where Evelyn wants to have her enrolled. The foster parents live just 25 minutes from Frank’s home, Frank will be entitled to scheduled visits, and Mary will be able to decide where she wants to live after her 12th birthday.
Mary is devastated at being placed in foster care, and her foster father says she refuses to see Frank. When Bonnie sees a picture of Fred up for adoption, she alerts Frank. Frank retrieves the cat from the pound and, learning that Fred was brought in due to allergy issues, realizes that Evelyn—who is allergic to cats—is overseeing Mary’s education in the guest house of Mary’s foster home. He then reveals to Evelyn—who had been a mathematician herself—that Diane had solved the Navier–Stokes problem, but stipulated that the solution was to be withheld until Evelyn’s death. Knowing that it meant everything to Evelyn to see Diane solve the problem, Frank offers Evelyn the opportunity to publish Diane’s work if she drops her objection to his having custody of Mary. Evelyn reluctantly agrees.
