Many years have passed since the colonized planet Darius was invaded by the alien Belser Army. A long distance distress call is received from the Solar System where the Darians first came from; apparently there were still Earthlings left on a colony on one of Jupiter's moons and they are now under attack by the Belser Army. The descendants of Proco and Tiat are enlisted to fly to the planets of the Solar System and save their surviving ancestors (IMDb.com).