Centuries ago a hardy band of survivors, fleeing a planetary catastrophe, took refuge in the inhospitable asteroid belt. Struggling for years to make what had once been short-term mining settlements into suitable colonies for permanent civilization, eventually they succeeded all too well, and their thriving population is approaching critical mass. Now they must make a choice: to go on as they are on the crowded but functional asteroids or to give up all they have worked for in a desperate plan t