"Gregor the Overlander" is a young adult fantasy novel by Suzanne Collins. The story follows a boy named Gregor, who lives in New York City with his family, including his two-year-old sister Boots. One day, while doing laundry in the basement, Gregor and Boots accidentally fall through a grate and end up in the Underland, a world located beneath the city's streets.

In the Underland, Gregor discovers that humans are not the only intelligent beings in the world. He encounters giant talking animals, including bats, cockroaches, and rats, who are engaged in a long-standing war against each other. Gregor learns that he is part of a prophecy that predicts he will help bring an end to the conflict and save the Underland from destruction.

Guided by a young girl named Luxa and a loyal bat named Ares, Gregor sets out on a dangerous journey to fulfill the prophecy. Along the way, he faces numerous challenges, including battling giant rats and fending off deadly predators. He also learns more about the history of the Underland and the reasons behind the ongoing war.

As Gregor and his companions get closer to fulfilling the prophecy, they realize that sacrifices must be made and that the outcome of the war will have far-reaching consequences. In the end, Gregor is faced with a difficult decision that will determine the fate of the Underland and its inhabitants.

"Gregor the Overlander" is the first book in a five-book series. The novel explores themes of courage, loyalty, and sacrifice, and is a thrilling adventure that will captivate readers of all ages.