Charlotte is a 12-year-old seventh-grader living in Pennsylvania who loves science and word puzzles. She feels isolated at school as she drifts apart from her closest friend and struggles to understand unspoken middle school social rules. Intelligent and logical, she frequently uses her online research to distract herself from her personal anxieties.

Ben is an 11-year-old sixth-grader living in Louisiana who identifies as logical and highly intelligent. Facing his parents' impending divorce, he decides to improve his social standing by running for student council. Lacking real-life friends, he relies on his online connection with Charlotte while enduring severe bullying at school.

Bridget is an artistic middle school student who has been Charlotte's best friend for years. She is becoming increasingly interested in popularity, boys, and fitting in with the artsy crowd. As her interests shift, she begins distancing herself from Charlotte and displaying mean behavior.

Magda is Charlotte's neighbor and fellow student in the talented and gifted program. Relentlessly bullied at school, she often isolates herself, choosing to eat lunch alone on the roof. She is deeply interested in science and poetry, possessing a kindness that others often overlook.

He is a retired art history professor who suffers a sudden medical emergency, prompting his hospitalization. He has a deep appreciation for art and birdwatching, which he tries to share with his daughter. His hospitalization is the central source of Charlotte's anxiety.

She is a statistician who is highly intelligent and logical. She takes on the responsibility of managing her husband's medical emergency while trying to support Charlotte through her fear and avoidance.

Ben's father is a brilliant chemist who announces his impending divorce from Ben's mother. He moves into a new apartment during the story and tries to maintain an open line of communication with his son, even when Ben shuts him out.

Ben's mother is a scientist who remains in the family home following the divorce announcement. She supports Ben's student council ambitions, helping him practice his speech and picking him up when he faces humiliation at school.

Wyatt is a logical and intelligent student at Ben's school who spends his lunch periods in the attendance office due to severe food allergies. He shares Ben's appreciation for logical puzzles and becomes a crucial real-life connection for him.

Theo is a student at Ben's middle school who actively bullies him. He frequently targets Ben with physical and verbal harassment, escalating his behavior during Ben's student council campaign.

Sherry is a student running for student council treasurer against Ben. She holds a grudge against Ben from elementary school after he reported her for cheating on a spelling test.

Mrs. Carlile is a friendly school employee who runs the attendance office. She provides a safe haven for students like Wyatt and Ben when they need an escape from the hostile cafeteria environment.

Sophie is a student in Bridget's art class who helps form the new art club. She is part of the popular group that hangs out at Red's pizzeria and becomes close with Bridget, displacing Charlotte.

Dee Dee is a student who joins the art club with Bridget and Sophie. She initially suggests that Charlotte would be a good addition to the club because of her intelligence.

Mateo is Magda's older brother, a high school student whom both Charlotte and Bridget have crushes on. He is fiercely protective and appreciative of his younger sister's unique personality.

Tori is a former friend of Charlotte and Bridget who achieved minor fame by going to spelling bee nationals. She now actively participates in bullying Charlotte alongside other students.

Gordo is Bridget's younger brother. He lacks a filter and directly asks Charlotte uncomfortable questions about her father's medical condition.