Eleven-year-old Gregor and his younger sister, Boots, return to the Underworld beneath New York City to find the cure for a terrible plague that threatens the life of their mother, as well as the lives of the people, bats, and rats who populate the underworld.

Everyone has been trying to keep Gregor from seeing "The Prophecy of Time". That is because the final prophecy calls for the warrior's death. With an army of rats quickly approaching and time running out, Gregor must defend Regalia and get his family back hom safely. There is a code that must be cracked, or all will be lost. It is a war designed to end all wars. The fates of the Underland and the great warrior, Gregor the Overlander, masterfully unfold...

An unobservant zookeeper is followed home by all the animals he thinks he has left behind in the zoo. En este cuento la gorila y otros animales escapan de sus jaulas y siguen al guardia a su casa a dormir.