With his tribe's move to follow the migrating bison, Yakari, the little Sioux boy, sets out on his own to follow the trail of Little Thunder, a wild mustang said to be untameable. Travelling far from home and deep into the territory of the terrible cougarskins, Yakari and Little Thunder undertake a great adventure and find their way back home.

While his friend Buffalo-Seed is in a deep coma and Rainbow reveals her shaman skills by keeping him alive, Yakari gallops off with Little-Thunder in search of the only living being capable of bringing him back to life: Buffalo-Seed's totem, the imposing, fantastic and dangerous Thathanka!