Lucy is a 12-year-old acquired savant who possesses both extraordinary mathematical calculation abilities and severe obsessive-compulsive disorder. Following years of comfortable homeschooling, she faces the terrifying prospect of attending seventh grade. She views the world entirely through numbers, frequently using the digits of pi to soothe her severe germaphobia and social anxiety.

Windy is an energetic, socially conscious seventh-grader who firmly believes in environmental activism and musical theater. She happily accommodates Lucy's strict cleaning routines without judgment. Her cheerful persistence pulls Lucy out of her isolated shell and into collaborative school projects.

Levi is a quiet seventh-grader who initially clashes with Lucy after copying her math test answers. Despite a sullen exterior, he possesses a sharp artistic eye and runs a website featuring candid photography of his classmates. He prefers the company of animals to most people.

Nana is Lucy's practical, deeply loving grandmother who stepped in as a parent after family tragedies. Recognizing that academic brilliance cannot replace human connection, she insists her granddaughter spend one year in public school before applying to college. She balances immense pride in Lucy with strict rules about participation.

Maddie is an image-conscious student who rules her social circle through exclusion and targeted cruelty. Under intense pressure from her mother to maintain a perfect physical and social profile, she lashes out at anyone who steps outside the norm. She specifically targets Lucy as a freak while trying to reclaim Windy's friendship.

Mr. Stoker teaches seventh-grade math with genuine enthusiasm. He quickly spots inconsistencies in Lucy's deliberately sabotaged test scores and actively tries to draw out her true potential. He runs a respectful classroom and encourages his students to apply logic to their everyday problems.

Paul is a Marine and Lucy's deeply admired uncle. He serves as an outside perspective on the family dynamic, firmly advising his mother that Lucy has grown far too comfortable avoiding the outside world.

Claire operates a chaotic but loving animal rescue center out of an old restaurant building. She gladly accepts the middle schoolers' offer to organize her severely backlogged adoption paperwork.

Windy's mother owns two day spas and maintains an immaculate personal appearance. Her focus on style creates a contrast with Windy's casual, messy lifestyle.

Maddie's mother is a controlling figure who openly criticizes her daughter's posture and diet. She prioritizes optics and physical perfection above emotional warmth.

Cutie Pi is an affectionate mixed-breed dog featuring a distinctive lightning-bolt mark on his fur. His arrival at the shelter tests Lucy's strict anti-germ policies, as his persistent friendliness challenges her to accept physical contact.

Ms. Fleming teaches social studies and language arts. She lacks the patience to accommodate Lucy's counting compulsions, pushing for compliance rather than understanding her student's neurological boundaries.

Windy's older teenage sister. She mirrors their mother's polished appearance, leaving Windy feeling somewhat like the odd one out in their household.

One of Levi's mothers. She works as a cardio instructor and runs a public relations firm, providing a warm and welcoming environment for her son's friends.