In Book 4 of the bestselling Underland Chronicles, Gregor is drawn ever deeper into a brewing crisis. It's only a few months since Gregor and Boots returned from the Underland, leaving their mother behind to heal from the plague. Though Gregor's family receives frequent updates on her condition, they all know Gregor must return to fulfill his role as the warrior who is key to the Underlanders' survival. Accompanied by his now-talkative, potty-trained little sister Boots, still considered the honorary "princess," Gregor joins forces with another princess — 12-year-old Luxa — and Ripred the rat to defend the Underlanders and the vulnerable "Nibblers" or mice, from the rat army. 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.