On Caprona, the Property that point Forgot, all the world’s savage past still lived. Right here were dinosaurs and traveling reptiles, here were the most primitive of cavemen, and the last of the Bronze Age group barbarians. But there is one more magic formula which the claws and fangs and sharp-edged spears guarded primarily.

This is the story of the man who tried to find that final secret. When Bradley, the adventurer, dared to combination the last terrible barrier to the center of Caprona, he entered an environment of wonder, terror, and danger beyond the creativity of any man-except Edgar Rice Burroughs.