Reynie is an 11-year-old orphaned boy possessing exceptional intelligence, logical deduction skills, and a strong sense of moral integrity. Growing up isolated in an orphanage, he is highly sensitive to the feelings of others and deeply fears being alone. He acts as the natural leader of his newly formed team, tasked with infiltrating the Learning Institute for the Very Enlightened.

Sticky is an 11-year-old runaway with a photographic memory that makes everything he reads stick in his head. Though brilliant and a former quiz show champion, he is timid, anxious, and deeply lacks self-confidence due to his difficult family past. He constantly polishes his glasses when nervous but slowly discovers his own bravery through the support of his new friends.

Kate is a 12-year-old girl who grew up in a circus after her mother died and her father vanished. She is highly athletic, fearless, and possesses an innate ability to accurately judge distances and weights by sight. She always carries a red bucket filled with useful tools like a rope, spyglass, and slingshot, preferring to rely solely on her own physical capabilities rather than asking for help.

Constance is a remarkably small, exceedingly stubborn girl found secretly living alone in a public library. She is highly sensitive, often irritable, and frequently exhausted. She covers her lack of knowledge by composing impromptu rhyming poems to express her displeasure or avoid answering questions directly. Her uncooperative nature frequently frustrates her teammates.

Mr. Benedict is a gentle, humble, and brilliant man who recruits gifted children to help him stop a global threat of mind control. He suffers from narcolepsy triggered by strong emotions, frequently falling asleep when he laughs. Having grown up as an orphan himself, he is deeply empathetic toward the children and firmly believes in their unique abilities when adults have failed.

Mr. Curtain is the narcissistic and malicious founder of the Learning Institute for the Very Enlightened. He uses a motorized wheelchair, wears dark glasses, and employs secret subliminal messages to manipulate the public into a state of continuous panic known as the Emergency. He plans to take control of the world's minds using top-performing children as filters for his machines.

Milligan is a sad, quiet man who works as an assistant and bodyguard for Mr. Benedict. He is a former secret agent who lost all of his memories after being kidnapped, retaining only his exceptional physical and tactical skills. He is highly capable in hand-to-hand combat, disguise, and escaping restraints.

Number Two is a highly efficient and devoted assistant to Mr. Benedict. She helps administer the peculiar tests used to recruit gifted children and assists in running operations from Mr. Benedict's home. She rarely sleeps, eats constantly to maintain her energy, and is fiercely protective of her employer.

Rhonda is a brilliant young woman who works as one of Mr. Benedict's closest assistants. She possesses a youthful appearance that allows her to pass as a child during the testing phases. She acts as a driver and liaison for the team as they leave for the Institute.

Miss Perumal is Reynie’s dedicated tutor at the Stonetown Orphanage. She recognizes his exceptional intellect and goes out of her way to provide him with advanced learning materials, speaking to him with respect and genuine affection.

Jackson is a cruel and condescending Executive at the Institute. A former top student who earned special privileges, he now enforces the school's bizarre rules. He openly relishes the power he holds over the younger students and the subservient adult Helpers.

Jillson is an Executive at the Learning Institute for the Very Enlightened. She leads classes where she teaches nonsensical lessons designed to plant subliminal messages in the students' minds, masking her brainwashing tactics as logical conclusions.

Martina is an extremely ambitious and combative student at the Institute who holds the coveted status of Messenger. She views newcomers with high test scores as a personal threat and goes out of her way to antagonize anyone who might challenge her position.

S.Q. is an Executive at the Institute who is somewhat less hostile than his peers but remains utterly devoted to his superiors. He has exceptionally large feet, causing him to frequently trip and stumble over his own shoes.

Corliss is a student at the Institute who acts as an exemplary pupil but harbors deep internal terror. His visible distress when summoned for punishment provides the main characters with an early warning about the school's psychological tactics.

Harry is a facilities inspector who visited the Institute and subsequently had his memories wiped. He now works as a miserable, subdued Helper, completing menial tasks with no recollection of his past life, family, or identity.