A reluctant young boy is pulled into a vast subterranean world where humans live alongside giant, intelligent animals and must fulfill a dangerous prophecy; over the course of five linked adventures he searches for his missing father, confronts warring rat armies and deadly plagues, forms fragile alliances with bats, cockroaches and other allies, and learns harsh lessons about leadership, family loyalty, and the moral costs of war while striving to protect both his loved ones and a fragile underground civilization.