Twelve-year-old Biddy, a spirited girl braving the Arizona heat with her trusty burro Buck, spends her days exploring the desert. Despite her polio and leg brace, Biddy and Buck embark on imaginary adventures until they stumble upon a mysterious cave. Inside, she discovers a peculiar machine and meets Joe, a man claiming to be from the "sky bloc."

Joe's miraculous healing powers restore Biddy's leg, igniting wonder and fear in the small town of Sage Bend. As tensions rise, the town's suspicion and prejudice lead to a dramatic confrontation, testing Biddy's courage and the power of hope.