A long dormant volcano explodes, freeing the ancient evil known only as the Locust, and filling the land with soot and ash. Alone and frightened, the Bone cousins, Thorn and feisty old Gran'ma Ben must fight the elements and the rat creatures as they struggle to reach the glorious city of Atheia. A pivotal and surprising new novel in the adventures of the Bone boys, caught between their desire to get home and a sense of duty for their newfound friends.