Caitlin is a ten-year-old fifth-grader with Asperger's syndrome who finds it difficult to process the recent death of her older brother. She loves reading the dictionary, drawing in black-and-white charcoal, and maintaining her physical personal space. Because she struggles to read social cues and facial expressions, she often retreats to her brother's room to avoid the noise and chaos of daily life.

Harold is Caitlin's grieving father, mourning the recent murder of his son and the earlier loss of his wife to cancer. He finds it difficult to process his trauma and cries often, failing to maintain a strong emotional front. He wants to help Caitlin understand her brother's death but lacks the emotional energy to properly guide her through her unique needs.

Devon is Caitlin's older brother who was killed in a recent school shooting before the events of the novel. He was an aspiring Eagle Scout working on a mission-style wooden chest. He was deeply protective of Caitlin, understanding her Asperger's syndrome and nicknaming her "Scout" after their favorite classic movie.

Michael is a quiet first-grader whose mother was a teacher killed in the same school shooting that took Devon's life. He isolates himself on the playground and resists his father's attempts to bond over football. He forms a hesitant connection with Caitlin when she shares a gummy worm with him during recess.

Mrs. Brook is the school guidance counselor who works closely with Caitlin. She tries to teach Caitlin about empathy, reading facial expressions, and making friends. She provides a safe space for Caitlin when the classroom or playground becomes too overwhelming, though she regularly pushes Caitlin out of her comfort zone.

Josh is a fifth-grade student and known school bully who pushes other children around on the playground. As the cousin of one of the school shooters, he faces isolation and unspoken anger from the community. He acts out defensively, assuming everyone constantly judges him for the tragedy his cousin caused.

Mr. Walters is the middle school art teacher who recognizes Caitlin's artistic talent. He tries to encourage her to expand her artistic horizons beyond charcoal by introducing her to colored pencils and crayons.

Rachel is a fifth-grade girl in Caitlin's class who feels self-conscious about her facial injuries after a bike crash. She becomes the unintentional target of Caitlin's blunt honesty when Caitlin bluntly describes her injuries and moves her desk to the corner.

Michael's father is a grieving widower whose wife was killed in the school shooting. He attempts to bond with his young son by asking him to throw a football, though his efforts initially drive a wedge between them due to their differing grieving styles.

William H. is an autistic student at Caitlin's school who occasionally screams and eats dirt. Because Caitlin associates the word "autistic" entirely with his severe behaviors, she fiercely rejects the label for herself.

Laura is one of the popular girls in Caitlin's fifth-grade class. She abruptly rejects Caitlin's direct request to be friends, contributing to Caitlin's frustration with classroom social rules.

The physical education instructor at Caitlin's school who oversees the dodgeball games Caitlin hates. He makes an insensitive remark about autistic students when Caitlin objects to playing, though he later apologizes after Mrs. Brook intervenes.

Caitlin's mother passed away from cancer two years before the events of the story. Her death was Caitlin's first experience with permanent loss, shaping how the young girl logically understands the finality of death even as her family mourns.