When Gregor falls through a grate in the laundry room of his apartment building, he hurtles into the dark Underland, where spiders, rats, and cockroaches coexist uneasily with humans. This world is on the brink of war, and Gregor's arrival is no accident. A prophecy foretells that Gregor has a role to play in the Underland's uncertain future. Gregor wants no part of it--until he realizes it's the only way to solve the mystery of his father's disappearance....

Eleven-year-old Gregor and his younger sister, Boots, return to the Underland 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 Underland.

When twelve-year-old Gregor finally learns the ancient prophecy, which foretells his death, he must gather his courage to defend Regalia from the army of rats, take his mother and sister home safely, and fight his own dark side.