The Mystery Inc. gang investigate the Sheriff's claims of aliens in Crystal Cove who are pilfering all the town's high-tech devices for their spaceship repairs.
Professor Pericles, desperate for the Planispheric Disk and revenge on Mystery Inc., creates a herd of mutated skull cattle to destroy Crystal Cove and stop them once and for all.
When a motorcycle-riding robber known as the Dandy Highwayman kidnaps all the women of Crystal Cove (including Daphne), it's up to our heroes to put a stop to his rogue ways.
The Mystery Inc. gang heads south of the border to search ancient Mayan ruins for the burial chamber of the Hunters of Secrets and the Heart of the Jaguar.
The gang returns from their trip, and find that the whole town has been enslaved by Professor Pericles, Mr. E, Brad, and Judy. So the gang has to save the town, by causing an uprising.