This novel picks up where the first of the "Hyperborea" science-fiction series, "MIgrations," left off, and concludes the overall narrative. In the first chapter, the Guide reflects on his success at sending his rivals Nora and Desh away on their impossible mission to explore the waterless region around Mount Erebus. In a trance-like state, he retells the story of how he learned the truth about the human presence on Hyperborea, and gained the knowledge that has made him all-powerful. His abusive relationship with the adolescent Leyla is also depicted. In subsequent chapters, Nora's expedition to Erebus gets under way. She, Desh and Wild Man depart from the starving town of Good Hope and make their way to the first thermal hut in Dry Valley, where they are joined by Guna and the fugitive Leyla, who has stolen all the Guide's food. After an arduous journey, the five voyagers reach the edge of the Eastern Plain, where the fleeting sight of a distant geyser offers the only hope that the party will find any water in the frozen desert. After a walk of many days, during which the voyagers come close to death and Wild Man begins to lose his sanity, they reach the flanks of Erebus and are sustained by the discovery of water and food in a derelict Earth truck. Wild Man abandons Nora and her people, while Guna falls gravely ill. A map in the truck leads Nora to a remarkable realm on the far side of Erebus, the Deep Thermal Valley, filled with food, water and paradisiacal warmth. In the valley, and also in the depths of the mountain, Nora and her companions discover fantastic marvels and a pair of lost races that hold all the secrets of the dying planet. Armed with new knowledge of humanity, of themselves and of their world, Nora and Leyla return to Good Hope with the children that have been born to them after many years in the Thermal Valley, resolved to challenge the patriarchal supremacy of the Guide once and for all, and to institute a new enlightened order for the pitiful human remnants of Hyperborea.