Growing to over 12 feet long and 1300 pounds, the prehistoric white sturgeon is a true freshwater giant, but because of human activity, its populations are now in decline. Cyril and his crew embark on a dangerous, action-packed mission to help scientists protect them. But to find this massive animal, the team must search the raging mountain rivers and dive beneath their frigid waters, all while avoiding bears, rock slides, freezing temperatures and deadly currents.