Earth is invaded by the criminal organization known as Makuu, led by Don Horror, who had first destroyed a space colony near Earth. Don Horror wants to dominate the whole universe, and the Earth represents an obstacle that he has to overcome by turning it into heaven for all evil. In response to Makuu's attack, Space Sheriff Gavan of the Galactic Union Police (銀河連邦警察 Ginga Renpō Keisatsu?) is deployed to Earth to defend his mother's home world. Gavan is helped by Mimi, the daughter of Commander Qom, and is given information by Qom, assisted by Marin on his home planet. Gavan goes to Earth to defend it against Don Horror and his devilish schemes. He settles on Earth incognito as Retsu Ichijouji, taking a job at the Avalon Youth Club in Japan to track Makuu's forces down.