Mystery Inc. is a group of mystery solving teenagers and their dog Scooby-Doo.
At Mystery Inc.'s Clubhouse, Velma Dinkley showed Norville Rogers and Scooby-Doo a newspaper showing a food festival was on at Keystone Castle. Daphne reminded them that they promised to help her cousin Anna Blake at the St. Louis High School talent show. Once arriving, Daphne goes alone, Shaggy and Scooby go together and Velma and Fred go together. Velma and Fred meet Coach Hayes. When Coach Hayes leaves, skeletons attack the two. Shaggy and Scooby find Anna, who warns them of the Phantom of the High School Musical. Scooby meets up with Daphne, leaving Shaggy alone. Later, they trap the phantom, actually Coach Hayes. He wanted to stop the talent show because the sports night was on at the same time.
Fred takes them to Toy Town to practise eating. Unfortunatly for Shaggy and Scooby, a giant robot has closed the park down. After exploring the amusement park, they venture into town. Tim Toiler, a mysterious man. Shaggy and Scooby find Tim's hat in the Toy Factory. Tim ended up being the villain.
The gang finally arrive at Keystone Castle, but it is deserted. They meet Costington, who is a suspect behind a giant Witch Queen. Shaggy and Scooby venture into the woods, since the Baron sent them. Monsters attack them. Later, the collapses and the Witch Queen is revealed to be real.