The Blieder drive, a faster-than-light drive system, has permitted the population of Earth to colonize the galaxy. Each planet has become home for a particular social group. Four hundred years after the diaspora (the "Great Explosion" of the title), a spaceship from Earth visits three of the planets, the first steps to unifying the galaxy under a new Empire. The ship contains two thousand Terrans including many pompous officials, an army of bureaucrats, a military force and the ship's crew, including some misfits. Things do not go entirely as hoped, as the incompetent military authoritarians of the ship encounter three very different societies.
