Gregor and the Marks of Secret (The Underland Chronicles 4)

Gregor has a crisis. For generations, rats have run the mice out of the lands they’ve claimed, keeping them on the move. But now the mice have started to disappear, and the young queen Luxa wants to know why.

When Gregor joins her on a mission to find out why the mice have disappeared, the true fate of the mice is revealed. It is something far more sinister than they had imagined…