Ickis, Krumm, and Oblina are saddled with babysitting the Gromble's nephew, Bomble. They take him along on a garbage hunting trip to a local hospital where the baby monster is accidentally switched with a new-born human baby. The trio must track down the Bomble at the home of his new human ""parents"" and replace him with the human. A new carnival opens near town and The Gromble is insulted and outraged by one of its attractions - the ""Monsters Are Fun"" ride. He assigns his two top students, Oblina and Krumm, the task of scaring its riders and shutting down the attraction.