The Shrouded Planet: Robert Randall (Robert Silverberg and Randall Garret)

Book I of Nidorian. The people of Nidor lived by the Law and the Scripture, remembering always the Great Cataclysm has nearly destroyed their world only five thousand years before. They gave thanks daily to the Great Light that had spared their ancestors and knew that only respect for tradition would keep their children safe. Then the strangers arrived - falling from clouds and clothes in light. They called themselves Earthmen...Cover art by Walter Velez.