The Galactic Federation is concerned about the number of wars on the Planet Earth. It sends three agents to determine if the planet is a potential threat to the universe, and whether it should be destroyed. The instrument of destruction is a device resembling a large black ball with two antennae that is variously called an anti-proton bomb, a solar bomb, and a neutron bomb. The agents (Captain Bokko, Nokko, and Pukko) are originally humanoid in appearance, but upon arrival on Earth they take on the appearances of a rabbit (Bokko), a horse (Nokko), and a duck (Pukko) that they had captured as examples of Earth life forms. While on Earth they travel in a tire-shaped vehicle capable of enormous speeds called the Big Wheel, which can travel on both land and water (and, with modifications, through the air)
