Daniel is a 12-year-old boy who moves to the quiet town of Noble's Green with his family to care for his sick grandmother. Possessing a keen, observant mind and an interest in Sherlock Holmes, he quickly realizes his new friends are hiding extraordinary abilities. Feeling ordinary compared to them, he relies on his deductive reasoning and investigative skills to understand the mysteries of the town. He actively questions the strange rules the superpowered children blindly follow.

Eric is a 12-year-old boy who serves as the unofficial leader of the superpowered children of Noble's Green. He possesses the abilities of flight and super-strength, which he quietly uses to protect the town from hidden dangers. He tracks his good deeds on a map in his bedroom, hoping that performing enough heroic acts will prevent him from losing his powers when he turns 13. He lives with his mother and her ex-boyfriend, carrying the memory of his deceased father.

Mollie is the first superpowered child Daniel meets in Noble's Green. She shares the power of flight with Eric but approaches situations with fierce instinct rather than calm planning. Frequently wearing torn jeans and a guarded glare, she maintains a tough exterior that hides a deep concern for her friends and anxiety about their impending 13th birthdays.

Herman Plunkett is an aging businessman and the original creator, author, and illustrator of the Johnny Noble comic books. He lives locally in Noble's Green and possesses a deep knowledge of the town's history. He provides Daniel with original comic sketches that help the boy investigate the mysteries surrounding the town's superpowered children.

Rohan is a quiet, highly observant boy with heightened senses. His powers allow him to hear distant smoke and sirens, and to view the moon as though looking through a high-powered telescope. He dresses formally and speaks with the vocabulary of a miniature adult. He approaches life philosophically, accepting the impending loss of his powers at age 13 as an unavoidable fate rather than fighting it.

Clay is a burly, imposing bully who possesses super-strength. Unlike Eric's group, he uses his abilities to intimidate others, steal belongings, and destroy objects in the local junkyard where he spends his time. He operates outside the moral rules followed by the other superpowered kids, fearing only Eric, who can match him in physical combat and exploit his fear of heights.

Louisa is a soft-spoken, traditionally feminine girl who can become incorporeal and move through solid objects. Unlike her peers, she views her powers as a burden and actively looks forward to turning 13 so she can live a normal life. She views Daniel's ordinary existence as an ideal she hopes to reach.

Simon is a young superpowered boy approaching his 13th birthday. His impending transition serves as an immediate example of the mysterious phenomenon that causes the kids of Noble's Green to lose their powers. Daniel stays with him during a sleepover to observe what happens when a child ages out of their abilities.

Michael is a former member of the superpowered group who recently turned 13. He has lost both his abilities and all memory of them, feeling physically sick whenever he attempts to recall his past feats. He drifts away from the group, fully integrating into the regular student body.

Daniel's grandmother is an ailing woman battling cancer. The family relocates to Noble's Green specifically to provide her with care. She occasionally stares out at the distant mountain with a dreamy expression, holding an unspoken connection to the town's history.

Daniel's mother and father relocate the family to a small town to care for their sick relative. They manage the household and medical care, remaining entirely unaware of the supernatural occurrences happening among the town's youth.

Daniel's younger brother is an energetic child prone to getting into trouble. His near-accident with a moving truck prompts the first display of Mollie's superpowers that Daniel witnesses.

Bud is Clay's sidekick. He possesses the ability to create a stink cloud when he becomes emotional, a lesser power that makes Clay feel superior. He follows Clay's orders without question.

Johnny Noble is the original superhero of Noble's Green who rescued children from an orphanage fire seventy years ago. He is the subject of local legends and comic books. The children hope he is the one super who managed to keep his powers into adulthood.