The Last Kids on Earth and the Destructor's Lair - By Max Brallier

Jack and Quint are trapped in the Monster Dimension! Their mission: prevent Rezzoch the Ancient, Destructor of Worlds, from reaching Earth and annihilating civilization. To do this, they must secure an audience with a creature more mysterious than any other. It's a race against time—and a race through the monster dimension! But before they can get back home to June and Dirk, Jack will find himself in a confrontation that will change everything. . . .