The adventures of a daydreaming, jazz-loving, football-headed 9-year-old, who lives in a boarding house with his grandparents and some eccentric boarders, encounters life in the city with his best friend Gerald, a loofah-haired kid, who is the keeper of the urban tales and coolest kid in class; and Helga, who torments him, but loves him secretly.
Arriving home from a basketball game, Arnold Shortman (Spencer Klein) and his best friend Gerald Johanssen (Jamil Walker Smith) learn that Alphonse Perrier du von Scheck (Paul Sorvino), the CEO of FutureTech Industries (FTi), has announced plans to redevelop the entire neighborhood as a luxurious high-rise shopping mall. That night, Helga Patiki (Francesca Marie Smith) finds that her father, Big Bob (Maurice LaMarche), is working with FTi to build a new super-sized branch of his beeper store in the proposed mall. She ultimately sides with her father, though is hesitant to do so because of her love for Arnold.
When Arnold and his crew win a trip to San Lorenzo, their adventure in the wild forces them to take the same risky path as Arnold’s missing parents.