Summary

Gregor and his two-year-old sister, Boots, fell through a... hole (?) and into the secret (kinda) underground world called the Underland (kinda obvious name). They learn of the Prophecy of Gray, and has to go on a quest to save their dad, who disappeared from their apartment two years ago and apparently fell through the same air duct as Gregor and Boots and has been imprisoned by the rats.