Major Gabriel Drum has returned to Earth. Thought long-dead, he brings news of the apocalyptic variety: only 666 people will survive the destruction of Earth, and President Stephen Blades is tasked with choosing them. Meanwhile, the Builders teleport the crew of the Clarke back outside the asteroid belt-everyone but Astra. The crew faces a tough choice-try to get home with their dwindling fuel, or use it in a last-ditch effort to save Astra?