Follow Gregor in fourth gripping adventure in Suzanne Collins's masterful New York Times bestselling Underland Chronicles!Now, in the fourth book in Suzanne Collins's New York Times bestselling series, Gregor is drawn into a crisis. For generations, rats have run the mice--or "nibblers"--out of whatever lands they've claimed, keeping them on the move. But now the mice are disappearing, and the young queen Luxa is determined to find out why.When...