Kyal Reen and his partner Yorim Zeestran are among the scientists, adventurers, and early colonists who arrive with a supply ship at Explorer 6, an orbiting headquarters for the scientific and archeological research being conducted across Earth, where the Venusians have had a presence for 18 years. Earth is a world very different from Venus, with its hot lava plains, steamy swamps, and murky, vaporous atmosphere. Kyal is a specialist in electrical spacecraft propulsion technology, and Yorim in synthetic gravitation. Both fields are applications that follow from the electrical nature of matter, an area of theory in which Terran science has so far been thought to be curiously deficient. However, that belief may have been premature. Kyal and Yorim have been sent to investigate some unusual structures discovered on the lunar Farside that suggest the Terrans might not have been so far behind after all.
They spend an initial period of rest and acclimatization after the voyage from Venus touring several locations down on the surface, meeting new people, and learning more from various sources about the story that is being put together of the enigmatic Terrans and their history. Although they were capable at times of amazing creativity and artistic expression, the races of Earth seemed driven by a compulsion toward violence and war that Venusians have been virtually free from, and which they are unable to relate to. Studies of Terran geology, scientific works, and ancient records reveal that at the time of the earliest history of the Terran race, Earth was involved in cataclysmic events that periodically disturb the Solar System. The skies that filled the early Terrans with awe and terror were very different from the quiescent conditions seen today. Without the scientific knowledge to understand what they were seeing, the ancient Terrans interpreted the spectacles in the heavens and the devastation that accompanied them as the actions of wrathful, vengeful supernatural beings, and this gave rise to the rituals and religions that set the tone for the belief systems and world view of the cultures that emerged after the period of worldwide catastrophe abated.
In his travels, Kyal meets a molecular biologist called Lorili and becomes involved in complications of her personal life that trace back to when she was a political activist on Venus. She is involved in another puzzling aspect of the work, which follows from Venus being a much younger planet. The forms of Venusian life that ought, from biochemical considerations, to have greater potential for complexity are in fact the more primitive, while the more advanced forms, including the Venusians themselves, have more in common with the genetically inferior pattern that characterizes the life forms of Earth. The concept of pure materialism and nothing more adopted by later Terran science as an adequate explanation for all of reality is also new to the Venusians, who never experienced the reaction against myth-inspired religions that was largely responsible for it. While most Venusian philosophers remain skeptical, the ideology that follows from such radical ideas is attractive to the leaders of a growing political movement calling for change, who admire and seek to emulate the Terrans' readiness not to shrink from force to achieve their aims. But was the Terran reality quite the way that things like recovered news accounts and political exhortations from those vanished ages depict?
The Terran constructions on lunar Farside turn out to be far more than a research and testing facility that was first supposed. Discoveries of deeper subsurface levels and signs of military combat in the surrounding area reveal it to have been a secret survival center created for selected elites as Earth was approaching its final, disastrous war. Could the similarities between Terrans and Venusians be due to the survivors migrating to Venus when Earth was rendered uninhabitable? The answer seems to be definitely no. Even though it is now pretty much established that the time scale the Terrans derived for the evolution of Earth were greatly exaggerated, there was no overlap. The Terrans were extinct long before life emerged on Venus. But there is a different, unexpected answer to the riddle.