From the distant planet of Popilloli comes the little boy Yatata to go to school. He is followed by his close friend, the great space horse, Davalon. Astro Boy and Yatata become pals but when the world learns of the unusual horse at Astro Boy’s house a vast throng surrounds them. Meanwhile, Trickum, a circus owner, realises that he could make a fortune if he had Davalon in his show and so he hires Ugapug, a gangster, to kidnap the horse. Astro Boy fights off the gang, but Yatata and Davalon realise that as long as they remain on Earth they’ll be hounded by curious people. They decide to return to Popilloli. But the gangsters follow them to the planet and try to round up the whole herd of great space horses. Astro Boy arrives in time to join the terrific fight in defense of the horses. Finally, the gangsters are defeated and sent back to Earth. Astro Boy watched as Yatata and the great space horse decide to move on to a much more distant planet where they hope to continue living in peace.