Jin, the neuter protagonist of Necessary Ill, begins the novel as a designer of plagues intended to set the world back into balancea balance of population and resources, creation and destruction, choice and certaintya balance more important to it than any individual life, including its own. Sandy, a young woman thrust violently out of her farm life into the dispassionate science of neuters like Jin, discovers her own need for balancea balance of safety and adventure, art and science, self-protection and love. But Jin and Sandy find that human life is full of change, and as the world is thrown off balance for all, each questions their ruling assumptions and must learn to see in new ways for the survival of friends and enemies alike.