Gregor sails off on an underground ocean with only a few soldiers and their giant bats to hunt the Bane in the Labyrinth, an uncharted maze of caverns deep in the Underland's rat lands.

[10] 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.

[11] Gregor and his bond Ares'[a] 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.

[c][11][12] Shortly thereafter, Gregor is finally trying to face the reality of going home without Boots when she is suddenly returned to the palace, having been saved by Luxa, Temp, and an unnamed moth.

[13] As of 2018, editions have been published in Italian, Turkish, German, Portuguese, Bulgarian, Finnish, Spanish, Danish, Dutch, Swedish, French, Greek, Norwegian, Polish, Persian, and Chinese.

She remarks on how Gregor is "prepared to heartlessly slaughter The Bane" yet overcomes his "hatred for the rats that killed his sister", but must still "face charges of treason" for his apparent betrayal of his duties.

[8] Timnah Card of the Bulletin of the Center for Children's Books describes how Gregor is "disturbed to discover his unsuspected capacities as a warrior".

"[7] More generally, School Library Journal said, "This is a strong choice for fantasy fans, including reluctant readers, even if they're not familiar with Gregor's first adventure.

"[24] Kathy L. Fiedler of the Kutztown University Book Review called the novel "a hit with young readers, especially those who've enjoyed The City of Ember by Jeanne DuPrau".

"[11] Ed Sullivan of Booklist claims "...fans will not be disappointed with this exciting, action-packed sequel", although he also warns "readers unfamiliar with the first novel will be at a disadvantage [as] Collins assumes knowledge of the characters and developments from the first book".

That continuing realism wraps the mile-a-minute adventure in a satisfyingly complex political and social network and provides the whole with a compelling emotional foundation.

Throughout, the motivations and growth of individual characters drive the action..."[10] Glisson writes as well of how Gregor has "matured since his last adventure" and "learns to deal with the fact that he is a "rager," a deadly and efficient fighter.