After solving their last mystery at Spooky Island, the Mystery Inc. gang is back in Coolsville, where they are being honored with their very own exhibit at the Coolsonian Criminology Museum. However, when a masked villain steals costumes of classic monsters on display and brings them to life, the gang must come out of retirement to solve the 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.