 Guggen is not like the other rat-children. He hates the sewers and loves the fresh air on the roof, where he has emigrated. His mom is worried. What will become of this fresh-air-loving, guitar playing son of hers? She forces her husband, Roger Rotten to take Guggen on a father-and-son trip down the sewers to hunt for cheese. On their adventure they must conquer sewercats, gigantic spiders and alligators. At the end of the day, Roger must admit that he has learned as much of his son as Guggen of him.