Velma wins first prize at her elementary school science fair with a computerized robot that Velma has programmed to do exactly what it's told. When mysterious locker robberies occur, Velma is the prime suspect. Things get even worse when her robot goes on a deadly rampage.

The Gang goes to the Coolsville amusement park. Shaggy and Scooby are excited because they will be the first ones to ride Monster Mountain - a giant roller coaster - for earning the most raffle tickets. Will they survive the emergence of a terrifying ghost clown?