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.As a terrified child, geologist Kyle Stone watched her family die in the 1959 Hebgen Lake Earthquake near Yellowstone. Fighting a lifetime of fears, she is one of the scientists with a finger on Yellowstone's pulse. When a new hot spring appears overnight in the park and a noted naturalist is scalded to death, Kyle mounts an expedition into the Yellowstone backcountry to unravel the mystery. Accompanying her are Ranger Wyatt Ellison, former student and friend, and Dr. Nicholas Darden, volcanologist and former lover. More than just a volcano is heating up.Amid personal conflict, earthquakes uprooting the land, and poison gases killing wildlife, Kyle finds herself in the unenviable position of convincing park officials to evacuate Yellowstone before tens of thousands of people die. As the earth shudders, Kyle must also choose between past and present, and defeat her darkest terror simply to survive.