Meet Benedick "Benny" Tapley IV, a boy born with a dramatic medical destiny: he is officially the "Most Allergic Kid in the World." Trapped inside a hermetically sealed, ultra-sanitized Gothic mansion by an aggressively overprotective, billionaire mother, Benny's body reacts violently to an astonishing 756 out of 758 tested substances—ranging from everyday food to birthday candles. To survive the simple act of going to school, he must navigate the world clad in a literal suit of armor and a portable oxygen tank. Yet behind the medical mask hides a surprisingly high-spirited, resilient rebel longing for nothing more than a taste of normal childhood adventure

Benny’s mother. A woman of immense privilege, wealth, and high social standing, she becomes a fiercely obsessive, overprotective, and controlling mother. She jealously guards her family’s privacy inside the nineteenth-century Gothic "Tapley Manor" and fanatically pursues an entirely antiseptic environment for her son. She is easily flattered by national spotlight and media attention regarding Benny’s medical condition

Benny’s father. A local practicing physician at the Plainsview Clinic, he is a much more grounded, practical, and lenient parent than his wife. He frequently objects to Augusta's extreme restrictions—such as encouraging Benny to play outside or attend public school to socialize—though he often feels he has lost control over his own household to his wife's commanding personality.

A classmate of Benny's since the fourth grade who is both pretty and agreeable. Knowing that Benny enjoys spending his time alone writing in the school cafeteria, she thoughtfully gifts him a personal pen set and notebook.

A sharp, good-looking kid who is a bit on the wild side. He is a well-meaning but reckless friend who tries to surprise Benny at his 8th birthday party by smuggling in a live cocker spaniel puppy, inadvertently triggering Benny's severe animal allergy.