A group of drag-racing fanatics, members of a Los Angeles club, move into an old deserted mansion and set up shop, making it their headquarters. They hold a Halloween masked ball for the club's grand opening, and invite everyone to come dressed as their favorite monster! Oddly enough, the festivities turn sour when one of the bright youths discovers an impostor among them in the form of an honest-to-gosh live monster who's been hogging all the dances with the best-looking girls

A young girl is killed at the beach in Malibu. Professor Otto Lindsay suspects that it is some form of mutated fish. However, his son Richard, who was a good friend of the girl, thinks that it is a madman who has a grudge against Richard and his friends. Soon the list of victims grows.