For years, engineer Landen Keene has envied the Kronian colony among the moons of Saturn, which embodies the pioneer spirit that Earth has lost. Then a Kronian delegation arrives on Earth with newfound evidence that the planets underwent cataclysmic changes only a few thousand years ago. And a white-hot protoplanet which Jupiter has emitted is found to be on a collision course with Earth. Keene has to choose between escaping on the Kronian ship or making a desperate cross-continent journey to find a woman he didn't even realize he cared about--if she is still alive....