The book depicts the arrival of members of an alien species called the Fithp that have traveled to our solar system from Alpha Centauri in a large spacecraft. The aliens are intent on taking over the Earth.
Physically, the Fithp resemble man-sized, quadrupedal elephants with multiple trunks. They possess more advanced technology than humans, but have developed none of it themselves. In the distant past on their planet, another species was dominant, with the Fithp existing as animals, perhaps even as pets. This predecessor species badly damaged the environment, rendering themselves and many other species extinct, but left behind their knowledge inscribed on large stone cubes (called Thuktunthp, plural of Thuktun in the Fithp language), from which the Fithp have gained their technology. The study of Thuktun is the only science the Fithp possess. The Fithp are armed with a technology that is superior rather than incomprehensible: laser cannon, projectile rifles, controlled meteorite strikes to bombard surface targets, lightcraft surface-to-orbit shuttles the size of warships, etc.
Nominated for Hugo and Locus awards in 1986.