Little Sioux Yakari lives in the middle of a peaceful meadow with his parents and his loyal dog, Oreille Tombante. Anticipating terrible tornadoes, the elders order the tribe to break camp and follow the trail of the bison that have already started to leave the area. Before starting the journey, the hunters capture a herd of horses, from which the fiery Petit Tonnerre manages to escape. Listening only to his courage, Yakari pursues the indomitable mustang, with the hope of making him his friend. The boy is helped in his quest by Great Eagle, his animal mascot who has given him the ability to talk to animals. However, the bird cannot prevent the intrepid papoose from straying along the way. Distraught, Yakari's parents leave the rest of the tribe and rush into hostile territory to find him.