Josh and his pals, after saving many mixed up, time-twisted worlds now find themselves in the center of the earth, in a cavern full of mushroom people. They call themselves the 'Shrooms, and Azabeth, mistakes them for a delicious treat from her planet and takes a huge bite out of one of the taller 'Shrooms, which poisons her, leaving her in a weak and disoriented state. Now it is up to Josh, Irwin, Prism, and new friend Porcini, the Italian 'Shroom, to find the cure to the mushroom disease and save Azabeth from certain death. The journey won't be easy, however, because they will face many challenges within the deep, dark caverns. Nightmare Hollow, which is off-limits to all of the 'Shrooms, is an especially dangerous part of the caverns, and just exactly where our lovable heroes must journey to. It is there that they will learn of the history of time itself and confront the most frightening foe yet...the Muncher!