Yellowstone National Park, spring 2003: the world's tallest geyser, one that can lie dormant for fifty years, suddenly erupts, new cracks open in the ground, trails close as the soil overheats, and a group of bison drop dead from poisonous gas seeping up from below. Satellite images show something moving under the surface, and online rumors claim the Yellowstone supervolcano, a type of eruption that occurs on average once every 700,000 years, is about to blow. This film follows the scientists who spent thirty years mapping the caldera beneath the park to figure out whether that fear has any basis. It explains why supervolcanoes are classed a million times more powerful than the Hiroshima bomb, notes that over twenty have occurred in Earth's history and more than half of those in the United States, and walks through a timeline of Yellowstone's past eruptions. The central question driving the investigation: if the Yellowstone Caldera erupted today, could anyone survive it, and what would happen to the country around it.