Environmentalist Leanne Allison and wildlife biologist Karsten Heuer followed a herd of 120,000 caribou on foot, across 1,500 kilometers of rugged Arctic tundra, from Canada's central Yukon to coastal Alaska (the Arctic National Wildlife Refuge) and back again. They wanted to raise awareness of threats to the caribou's survival, if proposed oil and gas development goes ahead in the herd's calving grounds in the Arctic National Wildlife Refuge.