The legends of a fabled land of the lost have floated for centuries around the bazaars of North Africa and the sand-surrounded oases of the vast Sahara. They tell of treasure caravans that have never returned, of weird monsters forgotten by time, of savage peoples surviving out of antiquity. Eric Carstairs had heard these tales but until he met Professor Potter he did not really believe them. But the famous paleontologist had the location of the entrance to the Underground World pinned down, and wanted only a man of courage to fly him there. Carstairs and Potter took the chance—and pierced the pit to Zanthodon, a world within the world, where cavemen and cave-beasts roamed side by side with dinosaur-monsters of millions of years ago.

Beneath the trackless sands and shifting wastelands of the Sahara, there lies a world unknown to modern man, the underground land of Zanthodon. In its vast unmapped terrain are great jungles, strange seas and forbidding mountains, and there can be found many of the beings that have long since vanished from the surface of the earth: dinosaurs, flying monsters and primitive cavemen.

Beneath the vast and trackless Sahara there lies a cavern so immense the whole nations could be swallowed up within it. There reside in the eternal subterranean glow the last of the Cro-magnons and their rivals the Neanderthals, lost remnants of ancient surface empires, and hordes of beasts and beings from all the ages of prehistory. Into this world, Zanthodon, penetrated the soldier-of-fortune Eric Carstairs - and immediately became embroiled in tremendous adventures! Hurok the Neanderthal had learned the meaning of friendship from Carstairs and in return would lead an expedition of cavemen to the dinosaur-guarded city of Zar where Carstairs had fallen captive to a sadistic queen and her scheming advisors. High adventure as only Lin Carter can tell it!

Under the trackless sands of the Sahara lies Zanthodon. That vast subterranean realm is the final homeland of the one-time masters of the world's surface - great dinosaurs, mighty jungles, and the living bands of primitive peoples from Neanderthals to Ancient Minoans and even Barbary Pirates! It was into the cruel hands of those feared corsairs that Eric Carstairs' beloved cave-maiden, Darya the Cro-Magnon princess, had fallen. It was his mission to save her, as well as to keep his caveman friends and his professor guide from the innumerable dangers spawned in the unmapped wilds of the Underground World.