Steve Backshall heads south once more and into Yellowstone national park in the USA. This frozen wonderland is home to the continent's most iconic beasts. Top of the list is Steve's favourite animal, the grey wolf, but he will need all his tracking skills to catch up with this elusive predator. Steve's next challenge is to head into the back country to find North America's largest land mammal, the one tonne bison. This deadly defender gives Steve a much closer encounter than he had bargained for. Pushing into the heart of Yellowstone the Deadly crew discover some ingenious hunters. Finally Yellowstone's deadliest secret is revealed, a force of nature so powerful it could change the world as we know it - a supervolcano, whose next eruption is already 40,000 years overdue!