Kal Emerson et Steve Sloan ont trouvé un filon d'or à Thunder mountain, mais n'ont pas le sou pour l'exploiter. Ils sauvent Sydney Blair des mains d'un prospecteur ivre, et celle-ci, reconnaissante, persuade son père, Samuel, de financer l'exploitation de la mine. Pendant le voyage, Sydney semble tomber amoureuse de Kal, mais ce n'est que parce qu'elle le croit bientôt riche. Arrivés sur le site, ils découvrent une ville champignon et leur mine exploitée par Rand Leavitt. Sydney se détourne alors de lui.
Cowboy Larry O'Day et son acolyte Lucky Smith tombent sur une Barbara Hartwell désemparée, qui est sur le point d'être arrêtée pour le meurtre de son oncle. Avec Barbara derrière les barreaux, Larry est déterminé à trouver le vrai tueur et se retrouve bientôt au milieu d'un mystère impliquant des entomologistes allemands fous et un réseau de contrebande amenant des "filles en photo" chinoises à travers la frontière mexicaine pour les vendre à de riches célibataires chinois.
Scooby-Doo, Shaggy, and Scrappy-Doo are on their way to a Miss Grimwood's Finishing School for Girls, where they have been hired as gym teachers. Once there, however, they find that it is actually a school for girl ghouls. The pupils include Sibella, the daughter of Count Dracula; Elsa Frankenteen, the daughter of Frankenstein's monster, Winnie, the daughter of The Wolfman; Phantasma (usually called Phanty for short), the daughter of a phantom, possibly The Phantom of the Opera; and Tanis, the daughter of The Mummy - all parodies/tributes to the Universal Monsters of the 1930s-40s. Other residents of the school are a floating white hand; an octopus, who is the school's butler; Legs, a spider that helps with the upcoming volleyball match; Miss Grimwood, the headmistress; and her pet dragon Matches (who dislikes Scooby at first, but later becomes friends, and has a strong friendship with Scrappy). Shaggy and Scooby want no part of this at first, but eventually they agree to stay as teachers.
A rich gambler by the name of Barney Ingram's horse, Cloverdale III is stolen by creditor Emmet Fallon. The horse is eventually stabled and renamed Lightning, but under the condition that it will be trained by a young rider as a racing horse.
The orphanage St. Jude, directed by Irmã Maria, financial difficulties that can take you to lock and utter helplessness to their children. Irmã Maria, watching a cartoon, has the great idea that can save the institution: use the Trapalhões - unconditional friends of children - and ask them to do a show to raise funds to save their children. Didi, Dede, Mussum and Zacarias perform a special show attracting a large audience. The audience vibrates with the mess and play Quartet. But unfortunately the show attracted not only good people, but also a gang of evil bandits trying to steal the money raised from the show. Irmã Maria inadvertently realize what is happening, try to react, but the bad guys, the stronger the hold. Theater background, Didi see the confusion and tries in vain to help the novice. After fights, the bad guys can get away with the bag of money, leaving Didi and Sister Maria fainted. Dede, missing Didi on stage, get out your search and find the two desacordados. Didi, Dede and the novice out an incredible and tumultuous pursuit of the bandits in the hope of recovering the stolen money. On the way, Didi faces thousand adventures and confusion, and even a wizard attempts to disrupt. Realizing they are being followed, the bandits enter the Beto Carrero Rodeo to lose them. Dress up cowboys and try to escape Didi, scene making huge success with the turning of the public. In this confusion, Beto Carrero recognizes Didi and goes to her aid, chasing the bandits, and in an act of adventure and action, Didi retrieves the bag with the money and all come back to the theater. Meanwhile, oblivious to all the confusion faced by his companions, Mussum and Zechariah follow with the show. Come Didi, Dede and Sister Maria followed by bandits performing many fights. When all seems lost, the Trapalhões are saved by a mysterious weapon. Many applause, captured bandits. Sister Maria explains to the audience what really happened throughout the show. In this moment of complete joy, Didi realize you're with the wrong bag, no money. But sadness is short-lived, and a great surprise is reserved for the end.