Gregor and the Marks of Secret book by Suzanne Collins

In Book 4 of the bestselling Underland Chronicles, Gregor is drawn ever deeper into a brewing crisis. For generations, rats have run the mice out of whatever lands they've claimed, keeping them constantly on the move. But now the mice are disappearing and the young queen Luxa is determined to find out why.

Gregor and Boots join Luxa on a simple fact-finding mission. But when the true fate of the mice is revealed, it is something far more sinister than they had imagined -- and it points the way to the final prophecy Gregor has yet to fulfill. His abilities are put to the test in this suspenseful, action-packed penultimate installment of Suzanne Collins's thrilling Underland Chronicles.