Caitlyn is a seventh-grade student who recently moved from New York to rural Vermont. She likes order, dislikes being stared at, and initially tries to follow rigid rules for fitting in. Feeling out of place at the unconventional Mitchell School, she observes her new classmates and acts as the narrator documenting their search for a missing student.

Paulie is a former student at the Mitchell School who mysteriously disappeared before the start of seventh grade. To his classmates, he is a legendary figure known for elaborate pranks, such as sticking pencils in his nose and setting up a banana peel experiment. His absence leaves a massive void in the school's social environment.

Henry is a seventh-grade student who arrived in the third grade, making him a self-proclaimed "Unoriginal" among his peers. He relies heavily on facts to calm himself down when he feels overwhelmed. He holds onto a heavy secret regarding the school's financial future from the very first day.

Gabby is one of the Originals and quickly becomes a welcoming presence for Caitlyn. She is a devoted fan of the reality television show The Search for the Next Great Megastar, using its archetypes to make sense of the people around her. She carries personal grief from the loss of her father.

Fiona is a bold, outspoken member of the Originals who often wears pantsuits to express her power. She is fiercely individualistic and views Paulie as a rival in causing trouble. She refuses to feel embarrassed, even when knocked over by the school's aggressive goats.

Known as Mags to her students, Miss Magruder teaches humanities by drawing connections between the students' lives and ancient Greece. She uses philosophical concepts, like Plato's allegory of the cave, to challenge her students' assumptions about the world.

Mr. Farabi teaches math, science, and gym at the Mitchell School. He strives to connect his lessons to real-world applications, framing both the school's goat herd and the soccer team as interconnected ecosystems.

Principal Glebus is the head of the Mitchell School. She maintains a stern, authoritative presence, often dealing with the school's roaming goats and managing the fallout from student antics. Behind her tough exterior, she carries the heavy burden of trying to keep the underfunded school open.

Diego is an athletic, humorous member of the Originals class who loves soccer and holds deep school spirit. He frequently wears a neon green T-shirt that once belonged to Paulie, viewing it as a good luck charm.

Kiera, nicknamed Fuzzy by Caitlyn, is a kindergartener at the Mitchell School. She clutches a stuffed bunny, misses her mother during the school day, and relies on Caitlyn for comfort and storytelling during lunch.

Yumi is a seventh-grade student with pink hair whose family works as puppeteers. She participates eagerly in the class's varied activities and contributes to the collective memory of Paulie's past actions.

Timothy is one of the twins in the Originals class. He frequently engages in imaginative play, such as zombie-versus-werewolf games, with his brother.

Thomas is the other twin in the seventh-grade class. He participates in the class's chaotic games and helps build monuments to their missing classmate out of sticks and rocks.

Wendy is Caitlyn's mother. She moved her daughter from New York to rural Vermont for a new job, which she finds difficult, and she attempts to support Caitlyn through the awkward transition to middle school.

Sam is a student at the Mitchell School who recalls Paulie's initially ordinary appearance. He helps build the legends surrounding Paulie through his memories of their fourth-grade year.

Anna is an outcast at Caitlyn's old school in New York. Caitlyn frequently thinks of her when reflecting on how she treated others to fit in, using Anna's awkward behavior as a reference point for what to avoid.