The satiric and fantastic romance is set in an imaginary semi-tropical land in Antarctica inhabited by prehistoric monsters and a cult of death-worshipers called the Kosekin.

The main story of the novel is the narrative of the adventures of Adam More, a British sailor shipwrecked on a homeward voyage from Tasmania. After passing through a subterranean tunnel of volcanic origin, he finds himself in a "lost world" of prehistoric animals, plants and people sustained by volcanic heat despite the long Antarctic night.