The world-ship of Ydar was a monster, vast implacable, and set on a collision course with the Galaxy of Man. Giant starship and mobile world, Destiny of Ydar is both refuge and vengeance of a long-dead civilization which must be stopped, or worlds will die. The cooperation of the Ydarans is vital. Too bad they're caught up in a civil war just now. Too bad, too, that they've forgotten the rest of the universe exists...