Iris Heller, a teenager with Sensory Processing Disorder, runs away to compete in a national bake-off contest. In order to get there, she steals her mom's car, travels along the East Coast, and does the most terrifying thing of all - interacts with actual people! Iris has never been like other girls, but she's not about to start letting that get in the way.

Iris has this profound fascination for the musican Dave Matthews, and she feels a compelling need to compete in the bake-off for Dave. To compensate for nervousness, she has the habit of humming, beatboxing, and making musical contraptions out of items around her. It is this talent that gets noticed at several road stops along the way, which leads to her inevitable "gone viral" glory. At a donut shop, Iris sings like an angel. At a coffee shop, she plays a symphony using cups and the soda fountain. At a restaurant, she builds a glorious musical fountain out of dishes and pans. Iris is the kind of pure spirit who brings the best out of the world around her without knowing it.

Iris' mom (Maisy) and her best friend Eric set out to find Iris. All lives converge at Happy World, the Disney-esque paradise, where the bake-off takes place. Iris, whose life has been one of isolation and misunderstanding, finds out just how much she is loved. It doesn't matter whether she wins the bake-off, she's already won the biggest contest of all, triumphing in life.