This is known as the Great Migration - the most breathtaking wildlife spectacle on earth. We join more than one and a half million wildebeest and hundreds of thousands of zebra on their annual pilgrimage through the plains of Tanzania. In this episode, we find one of the few remaining packs of African Wild Dog in South Africa's Kruger National Park. We venture into the heat-hazed desert of the Karoo in South Africa, looking for the forgotten town of Nieu Bethesda.