Catastrophic wars have wiped out all animal life and destroyed the Earth’s atmosphere, leading to a constant shower of radioactive debris. Those who had the means to escape now live on other planets, served by humanoid robots (called androids, or “andys” for short) who do much of the hard labor. It is illegal for these robots to go to Earth; those who do are hunted down and “retired” by police agents, such as the book’s protagonist, Rick Deckard. The androids look and act almost exactly like humans, except that they. . .