Behind the Walls of Terra — Philip Jose Farmer

All they knew was that one of the dreamed Bellers had escaped to Earth, and so Kickaha and Jadawin's beautiful sister, Anana, had joined forces to track the evil one down. Their mission was far more dangerous than either of them expected, however. For the Lord of Earth, Red Orc, was being challenged by another Lord, Urthona. And both were perfectly willing to use Kickaha and Anana to further their own ends.