When David Innes and Abner Perry set out to search for mineral deposits in Perry's newly invented Mechanical Prospectro, they never dreamed of discovering the beautiful, terrifying world of Pellucidar five hundred miles beneath their feet. Cast into a country of fierce fighting men, beautiful women, and vicious beasts, David and Abner take sharply diverging paths. David and his mate, Dian the Beautiful, set out to teach Pellucidar the ways of civilization and succeed in gathering a number of primitive kingdoms into the Empire of Pellucidar. Meanwhile, Abner turns his inventive genius to the science of aeronautics, with dire results for both David and Dian.