Gregor and the Prophecy of Bane
Several months have passed since the events of the first novel, when Gregor and his baby sister Boots first fell into the subterranean city of Regalia (a part of the "Underland") and undertook a quest to save their father, who was being held prisoner by a group of Underland rats. The Underland humans supported the siblings' mission because they believed it was prophesied by their founder, Bartholomew of Sandwich.
During their journey, the questers are caught in a whirlpool, encounter an island of carnivorous insects, which results in Howard's bat, Pandora, being eaten alive, and are betrayed by the two shiners (fireflies) who were hired to provide them with light. Gregor himself begins to struggle with a new "power" that manifests when he is in battle. He is what the Underland creatures call a "rager", a person who is overcome by a kind of "battle-fury" when they fight, making them completely deadly even without training. Gregor and his bond Ares' worst trouble, however, is when they and the remaining questers become separated from the human queen Luxa, the cockroach Temp, and Boots during a fight with some serpents. The three missing are assumed dead, and Gregor finds himself emotionally frozen at the thought of having lost his baby sister. When he finally finds the Bane, he learns that it is not an adult monster, as was assumed, but instead a baby whose parents have just died. He can not bring himself to kill it, and so he and Ares take it to be raised by the only friendly rat they know: Ripred. After this, the two return to Regalia, where Nerissa has just been crowned queen. Shortly thereafter, Gregor is trying to finally face the reality of going home without Boots when she is suddenly returned to the palace, having been saved in turn by Luxa, Temp, and an unnamed moth. The two then return to the surface world.