A crew mutinies and throws their captain out of their spacecraft because he won't return to Earth. When they go through his notes and realizes that the Earth has become uninhabitable in the years they were in space, they rescue him.
Three broken men build a submarine that can bore through bedrock. They test it by boring under the ocean floor. There they find a civilization of sorcerers who have been ostracized from the surface world. The sorcerers use their magic to heal the men.