Two teenage cousins who assist an inventive relative develop experimental vehicles, including a hybrid flying road racer, find their routine upended by an eccentric inventor and a baffling case of a disappearing gun. The mystery propels aerial and ground pursuits that involve mysterious men, a driverless automobile, mid‑air rescues, exploration of an old mansion, and a long, fast-moving chase across varied terrain. Resourcefulness, inventive gadgets, and teamwork sustain the action as the youths confront dangers and unravel the plot, leading to a decisive resolution in which one young protagonist achieves a notable triumph.