<P> Gregor the Overlander is a children's epic fantasy novel . The book was written by Suzanne Collins and was published in 2003 as the first book of The Underland Chronicles . It was received well by critics, and was listed as one of New York Public Library's 100 Books for Reading and Sharing . It was featured by the U.S. National Public Radio in 2005 . Scholastic has rated the book's "grade level equivalent" as 4.9 and the book's lexile score as 630L, making it reading - level - appropriate for the average fourth or fifth grader . </P> <P> The novel has been published in several languages and is available as both an audiobook and ebook . Its United Kingdom edition was published under the alternate title Gregor and the Rats of the Underland . </P> <P> Eleven - year - old Gregor is left home alone in his family's New York City apartment to watch his sisters and grandmother . When Gregor's baby sister Boots falls through an old air duct grate in the building's basement, he dives in after her . The two fall miles below into the Underland: a subterranean world home to humans with near - translucent skin; giant sentient bats, rodents, and insects; and an escalating conflict between the human city of Regalia and the rats' King Gorger . They meet several "Underlanders", among them the Regalians' crown princess Luxa, her cousin Henry, and the bats who are "bonded" to them . At first, Gregor wants only to return home, but when he is attacked by two rats during an escape attempt and saved by the Underlanders, he inadvertently brings the conflict between the two groups to a head . </P> <P> It is then that he learns the real reason for the rats' hatred of Overlanders: a mysterious prophecy written by the human colony's founder Bartholomew of Sandwich hints that an Overland "warrior" will stop an attempt by the rats to take over the underground realm once and for all . The Regalian council believes Gregor to be this warrior, and tries to convince him to undertake the quest mentioned in the "Prophecy of Gray". Though he sympathizes, Gregor is reluctant to help until he learns a surprising fact: his father, who disappeared unexpectedly over two years before, had actually fallen down into Regalia just like Gregor and Boots and been taken prisoner by the rats . Gregor, his sister, and a group of Regalians go on a journey to rescue Gregor's father and recruit allies for a war against the rats . </P>

What is the main conflict in gregor the overlander
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