A masked villain wreaks mayhem on the city of Coolsville with a monster machine that creates real-life versions of Mystery Inc.'s former foes like The 10,000 Volt Ghost, The Cotton Candy Glob, The Skelemen and The Pterodactyl Ghost. Fred, Daphne, Shaggy, Velma and Scooby-Doo launch an investigation into the monster outbreak that leaves Shaggy and Scooby questioning their roles in Mystery Inc. Eager to prove their detective skills, the ever-ravenous duo comes up with a secret plan to solve the mystery all by themselves. Can the gang unravel their most challenging case?

When the Mystery Inc. gang is invited to Spooky Island, a popular amusement park, they soon discover that the attractions aren't the only things that are spooky. Strange things are happening, and it's up to Scooby, Shaggy, Fred, Daphne, and Velma to uncover the truth behind the mysterious happenings.