WHEN MAN FIRST REACHED OUT TO THE STARS, THE THURGS ARRIVED BEARING GIFTS. One was the Beam, a mysterious expressway to another part of the universe. The other was the ability to remove the brain from a dying person and install it in a substitute body - a 'subb'. At first the gifts were accepted with unquestioning gratitude. Then a few people began to wonder. By making it so easy to get to one part of the universe, were the Thurgs, in effect, keeping the rest of the universe hidden? And the subbs. did they remain human? Were the Thurgs deliberately stocking the universe with a new brand of being - one capable of erasing mankind?