Eleven-year-old Gregor and his younger sister, Boots, return to the Underworld beneath New York City to find the cure for a terrible plague that threatens the life of their mother, as well as the lives of the people, bats, and rats who populate the underworld.
As the plague in The Underland spreads, Gregor begins to understand his role in the Prophecy of Blood, and must summon all of his power to stop the biological warfare that is spreading a plague through the Underland.
