At the opening of the Coolsville Museum of Criminology, a masked figure steals the costumes of several of the gang's old enemies.
Scooby and the gang lose their cool – and their stellar reputation – when an anonymous masked villain wreaks mayhem on the city of Coolsville with a monster machine that re-creates classic Mystery Inc. foes like The Pterodactyl Ghost, The Black Knight Ghost, Captain Cutler’s Ghost and The 10,000 Volt Ghost.
Under pressure from relentless reporter Heather Jasper-Howe (ALICIA SILVERSTONE) and the terrified citizens of Coolsville, the gang launches an investigation into the mysterious monster outbreak that leaves Shaggy and Scooby questioning their roles in Mystery Inc.
The ever-ravenous duo, determined to prove they’re great detectives, don a series of far-out disguises in their search for clues. All signs point to Jeremiah “Old Man” Wickles (PETER BOYLE), the former Black Knight Ghost who was once unmasked by the gang and thrown in jail. Did the creepy wannabe launch the monstrous attack on Coolsville in a diabolical quest for revenge?
Meanwhile, brainy Velma (LINDA CARDELLINI) becomes smitten with another key suspect, Coolsonian Criminology Museum curator Patrick Wisely (SETH GREEN), as macho leader Fred (FREDDIE PRINZE JR.) and image-conscious Daphne (SARAH MICHELLE GELLAR) attempt to determine the identity of the Evil Masked Figure whose monster army is wreaking havoc on Coolsville.