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?.