Whe eleven-year-old Gregor follows his little sister through a gate in the laundry room he ends up the dark Underland beneath the city populated with humans living in an uneasy peace beside giant spiders, bats cockroaches and rats. He discovers a strange prophecy which fortells a role for him in Underland's future that will be the only way to solve the biggest mystery of his life and change him and Underland forever.