Mars is dying. In an epic undertaking, its declining population makes preparations to journey to Earth, a planet still inhabited by prehistoric life in our very distant past. Eris Moon, a spacecraft, is constructed by converting one of the moons of Mars.

As the date of the exodus approaches, Zymon Cates, a high-ranking reconnaissance pilot, crash lands at the southern ice cap and is held against his will by the mistrustful inhabitants of Kaa, a long forgotten underground city. Now Zymon must escape before Eris Moon leaves orbit forever, and while there is very little time, time is the least of his problems.

Meanwhile, Dex Pheetyr, a sociopathic killer, escapes from the Mars-based penal colony and stows away aboard the rescue ship sent to find Cates. What the presence of this single convict means for Eris Moon as well as the future of humankind on Earth could never be predicted.