When eleven year-old Gregor follows his little sister down a laundry chute, he hurtles into a dark, dirty Underland, deep beneath the New York City. There, humans live uneasily alongside giant spiders, vast cockroaches, huge bats and some appalling rats, but their fragile peace is about to fall apart. Gregor wants no part in the conflict between these shadowy creatures. He just wants to find his way home. But when he discovers that a strange prophecy reveals a role for him in the Underland's uncertain future, he realises it might be the only way to solve the biggest mystery of his life.