When Mystery, Inc. are guests of honor at the grand opening of the Coolsville Museum of Criminology, a masked villain shows up and creates havoc before stealing the costumes of the gang's most notorious villains: Black Knight Ghost, Pterodactyl Ghost and Tar Monster. Could it be that their nemesis, mad scientist Jonathan Jacobo has returned and is trying to recreate their deadliest foes? Velma has a crush on the hunk / museum curator Patrick Wisely but why is he acting so suspicious? The Mystery Gang is hard pressed to succeed this time, since pesky TV reporter Heather Jasper-Howe insists they are buffoons.