Plot

The gang has to battle police and parental involvement while trying to solve the mystery of a Slime Mutant who's trapping his victims in a gelatinous cocoon.

After solving another mystery, the gang gets arrested by Sheriff Bronson Stone for meddling and their parents are called in. Velma helps run the Spooky Museum her parents own by giving tours, explaining the mysterious "hauntings" and disappearances in the history of Crystal Cove to tourists and mentions the disappearance of the entire Darrel family on one Halloween years before. Fred tries to explain his love of mystery solving to his father, Mayor Jones, who tries to no dismay to guide him in another direction, and Shaggy and Daphne's parents share the same concerns. Meanwhile, miners mining underneath Fruitmeyer's accidentally bust through the old Crystal Cove caves and are attacked by a green glowing seemingly radioactive monster and kidnapped. While driving to school, Velma tries to discuss her and Shaggy's relationship, but Shaggy insists on hiding it, to her dismay. The gang is then attacked by the same monster, and follows it into the caves. Daphne finds an old locket with, unbeknownst to any of them, the photos of Judy Reeves and Brad Chiles. They find the "mummified" bodies of the miners in cocoons of radioactive green goop. Fred steals a body for research after Sheriff Stone refuses to listen. They bring it to Professor Raffalo at the school, who tells them the miner is alive but dehydrated, and that he wants to run tests on the cocoon. The gang goes to Fruitmeyer's for dessert, a green sort of dessert that looks like jell-o. Velma is agitated by Shaggy avoiding her, and Fred continues friend zoning Daphne out of ignorance. The professor, while running tests at night, is attacked and cocooned by the monster. At the radio station, the gang visits their radio host friend Angel Dynamite, a young hippie adult. Fred suffers from guilt over what happened to the professor and wants to give up. Scooby begins eating the cocoon sample Velma brought, realizing it's Fruitmeyer's dessert. The gang puts together that the monster is fake, and learn the Fruitmeyer hasn't been in town very long. Shaggy and Scooby pose as female employees at Fruitmeyer's, and help the gang sneak in late one night after Fruitmeyer leaves. They are then attacked by the monster, and Daphne is locked in the closet. Daphne accidentally falls down a hole that was drilled through the floor into the old caves. The gang realizes the hole leads right under the bank. Fred's trap malfunctions and traps the gang except Daphne, and they get "cocooned" in Fruitmeyer's. Daphne gets chased and barely manages to escape when Fred saves her by plastering the monster to the wall. The sheriff shows up, and the gang tells him the monster is Franklin Fruitmeyer, but it's revealed that Franklin Fruitmeyer is the one who called the sheriff after the silent alarm went off. The monster is revealed to be Professor Emmanuel Raffalo, who wanted to rob the bank and be rich and is then arrested. Daphne inquires about the locket, which the Mayor seems shocked to see, but the professor says he doesn't know what it is. At the radio station, Daphne is distressed about the locket, and Shaggy answers a radio call, but it met by a voice calling himself Mr. E who says the gang is doomed and should never have brought the locket out of the cave, and that they're too close to uncovering the truth of the curse of Crystal Cove.