Gregor and the Code of Claw

Everyone has been trying to keep Gregor from seeing The Prophecy of Time. That is because the final prophecy calls for the warrior's death. With an army of rats quickly approaching and time running out, Gregor must defend Regalia and get his family back home safely. There is a code that must be cracked or all will be lost. It is a war designed to end all wars.

The fates of the Underland and the great warrior, Gregor the Overlander, masterfully unfold in this thrilling and suspenseful final installment in Suzanne Collin's Underland Chronicles.

This description comes from the publisher. Gregor and the Code of Claw is the fifth book in the Overland Chronicles, the first of which is Gregor the Overlander.