The world's largest volcano does not reside beneath Hawaii's mountains, or in Washington state, but Yellowstone National Park. Past eruptions have darkened our continent and covered it with a blanket of ash that smothered both plant and animal life. Now the supervolcano, with its earthquakes and geysers, is monitored on a daily basis for signs of the beast reawakening. When a new hot spring appears overnight in the park and a noted naturalist is scalded to death, Kyle Stone mounts an expedition into the Yellowstone backcountry to unravel the mystery.