Since the Introdus in the twenty-first century, humanity has reconfigured itself drastically. Most chose immortality, joining the polises to become conscious software. Others opted for gleisners: disposable, renewable robotic bodies that remain in contact with the physical world of force and friction. Many of these have left the solar system forever in fusion-drive starships. And there are the holdouts: the fleshers left behind in the muck and jungle of Earth-some devolved into dream apes, others cavorting in the seas or the air-while the statics and bridgers try to shape out a roughly human destiny. But the complacency of the citizens is shattered when an unforeseen disaster ravages the fleshers and reveals the possibility that the polises themselves might be at risk from bizarre astrophysical processes that seem to violate fundamental laws of nature.