To save his tribe, the cannibal Stopmouth must abandon it. Leaving the stone-age world of the Surface behind, he travels to the Roof, the mysterious hi-tech world suspended above. But the Roof has its own problems. The nanotechnology that controls it is collapsing. And now a rebellion against the ruling Commission is about to erupt.
Hunted by the Commission's nano-enhanced agents, Stopmouth must succeed in a desperate hunt of his own: to find the woman he loves. Only she knows how to save his tribe. But in this super-sophisticated world, all he has to fight with are his raw strength and fierce courage.