Set in an ancient time, when humans were few and survival required a fighting spirit. It is a time of drought for the People of the Canyons. Plant foods have been exhausted and small game has disappeared from their hunting grounds. Trei convinces his father to gather a few hunters and attempt a bison hunt, a risky undertaking with their simple wooden spears. When the hunt ends in tragedy, Trei and his twin sister Souk secretly determine to travel north. A traveller has talked of a tribe who can throw a spear like a lightning bolt and bring down mammoth and bison. Trei and Souk must first escape their people, then begin the perilous journey north. But it is said that no one ever returns from the territory of the Manhunters.