The earth's core overheats. From Yellowstone to Sakurajima, thousands of cubic feet of magma spews into a summer sky. Ash plumes, miles high, incinerate most of the earth's inhabitants. In a bunker system deep in the Salmon River Mountains, a small band of survivors form the Undergrounders; among them, sixteen-year-old Derry Connelly, and a young Septite homesteader, Jakob Miller, who stirs up feelings inside her she didn't know were possible.When...