The story takes place on Earth starting in the year 2073. A group of alien beings called Ringnonians crash land on Earth. They are giant humanoid creatures over 9 feet tall. The Ringnonians offer to help humanity with their advanced technology. At first they are welcomed, but over time many humans grow suspicious and resentful of them. The story follows a group of aliens called Ringnonians who are forced to abandon their home planet of Ringnon due to a deadly plague. They establish colonies on other planets, including Earth and Kittan.

The Ringnonians face many threats including pirate attacks, dangerous jungle planets, and the continuing spread of the deadly plague. They race to find a cure for the plague and sufficient food supplies to enable their population to evacuate Kittan before it is overrun.

Return to Earth continues the Ringnonian Saga with Quanyo returning to Earth, war breaking out over disputed territory, the introduction of genetically engineered giant soldiers, and struggles for power amongst various alien factions now present on Earth.