For this was the inner surface, the land of Pellucidar, where evolution had taken a strange turn and man was slave to the monstrous Mahars. In a world where time and direction did not exist, David and Perry fought for existence against prehistoric dangers and the chance to bring civilization to this world of Eternal Noon. ...  It was a world back in the Stone Age, where prehistoric monsters still lived, and cave men and women battled against fierce inhuman masters.