Thrax plots to put a stop to the gang & capture Boober & Wembley and Terrence McBird is afraid. When Ma and Pa Gorg can't find Junior, they come to believe that Boober is their son transformed into a Fraggle by an evil sorcerer (whom is mentioned in "The Encyclopedia of Gorgish Myth and Wisdom" to reappear in their neighborhood on a specific day) and struggle to accept the changeling as the heirs to the Universe. It's up to our hero: Thidwick the Big-Hearted Moose to defeat Thrax, the Gorgs, and dozens of civil servants and Terrence is skeptical. Thidwick and Terrence must team up with the gang: Gobo, Mokey, Red, Yertle the Turtle, Fox in Socks, Mr. Knox, Jane Kangaroo, Junior Kangaroo, The Wickershams, and King Derwin.