Welcome to the fractured future, at the dusk of the twenty-first century. Earth has a population of roughly a billion hominids. For the most part, they are happy with their lot, living in a preserve at the bottom of a gravity well. Those who are unhappy have emigrated, joining one or another of the swarming densethinker clades that fog the inner solar system with a dust of molecular machinery so thick that it obscures the sun. Except for the solitary lighthouse beam that perpetually tracks the Earth in its orbit, the system from outside resembles a spherical fogbank radiating in the infrared spectrum; a matrioshka brain, nested Dyson orbitals built from the dismantled bones of moons and planets.