Gregor The Overlander

Description for GREGOR THE OVERLANDER by Suzanne Collins:

WHEN ELEVEN-YEAR-OLD GREGOR follows his little sister through a grate in the laundry room of their New York apartment building, he hurtles into the dark Underland beneath the city. There, humans live uneasily besides giant spiders, bats, cockroaches, and rats -- but the fragile peace is about to fall apart.

Gregor wants no part of a conflict between these creepy creatures. He just wants to find his way home. But when he discovers that a strange prophecy foretells a role for him in the Underland's uncertain future, he realizes it might be the only way to solve the biggest mystery of his life. Little does he know his quest will change him -- and the Underland -- forever.

This is #1 in The Underland Chronicles.