The city and the stars

Men had built cities before, but never such a city as Diaspar; for millennia its protective dome shutout the creeping decay and danger of the world outside. Once, it held powers that rules the stars. But then, as legend had it, The invaders came, driving humanity into this last refuge. It takes one man, A Unique to break through Diaspar's stifling inertia, to smash the legend and discover the true nature of the Invaders.