Gregor falls through a grate into the Underland, a world of giant creatures and impending war, where he must confront a prophecy to find his father. Gregor, a boy from the human world, is thrust into the subterranean realm of the Underland, a place populated by giant spiders, rats, and cockroaches who live in an uneasy truce with humans. This world is on the brink of war, and Gregor's arrival is foretold by a prophecy that designates him a key figure in its future. Driven by the desire to uncover the truth about his father's disappearance, Gregor reluctantly embarks on a perilous quest that will irrevocably alter both his own destiny and the fate of the Underland.

The premise sets up a classic adventure narrative with a reluctant hero fulfilling a destiny. The inclusion in the Scholastic Gold line suggests it is a well-regarded children's or young adult novel. The description highlights suspense and adventure, indicating a fast-paced plot. The comparison to the author's later work, The Hunger Games, implies a certain level of thematic depth and engaging storytelling.