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It is notable for its depiction of an American President whose effectiveness is compromised by his fundamentalist religious beliefs, which are manipulated by the aliens.
Other memorable scenes and events include the discovery of an alien in the desert, who clearly says in English, "I'm sorry, but there is bad news," and this alien's subsequent interrogation and autopsy; the discovery of an artificial geological formation and its subsequent nuclear destruction by a desperate military; spider-like self-replicating machines; and the Earth's eventual destruction.
There is another alien faction at work, however, frantically collecting all human data, biological records, tissue samples, seeds, and DNA that they can, and evacuating a handful of people from Earth, of whom some eventually settle a newly terraformed Mars while others 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.
The two books show at least one solution to the Fermi paradox, with electromagnetically noisy civilisations 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).