The novel features scenes and events, including the discovery of a nearly-dead alien in the desert, who clearly says in English, "I'm sorry, but there is bad news," and the alien's subsequent interrogation and autopsy; the discovery of an artificial geological formation and its subsequent nuclear destruction by a desperate military; and the Earth's eventual destruction by the mutual annihilation of a piece of neutronium and a piece of antineutronium dropped into Earth's core.
There is another alien faction at work, however, represented on Earth by small spider-like robots that recruit human agents through some form of mind control. They frantically collect all the human data, biological records, tissue samples, seeds, and DNA from the biosphere that they can and evacuate a handful of people from Earth. In outer space, this faction's machines combat and eventually destroy the attackers but not before Earth's fate is sealed. The evacuees eventually settle a newly terraformed Mars while some form the crew of a Ship of the Law to hunt down the home world of the killers, a quest described in the sequel, Anvil of Stars.
One of the point of view characters is Arthur Gordon, a scientist. He; his wife, Francine; and son Martin are among those rescued from the destruction of Earth. Some other characters are close to an American president, who fails to take action against the threat.
The two books show at least one solution to the Fermi paradox, with electromagnetically noisy civilizations being snuffed out by the arrival of self-replicating machines designed to destroy any potential threat to their (possibly long-dead) creators. (A similar theme is explored in Fred Saberhagen's Berserker novels.)