Dick Harbinger (Joe Don Baker) is in the police and is obsessed with stopping history repeating itself. Thirteen years earlier a man wearing a pumpkinhead and driving a lawnmower committed vile murders on some children. The night is Halloween and everyone is a suspect. The school janitor, Zeke, is a suspect and is questioned. Throughout the film, when the word "geek" is used, he reappears and corrects the speaker saying, "it's Zeeeeke." The father of the family (George Kennedy) is too obvious a suspect and is questioned by police. He is usually caught by his daughter Mary, trying to creep into the bathroom when she is showering, or peering in her window whilst she is sleeping. His daughter catches him and screams and always says the same line, "Damn it Daddy, what are you doing?" Kennedy always replies, "I'm just, erm, mowing the lawn." The daughter replies always the same, "sure Daddy, that's what you always say." Mary's friend Rosie is dating Tony "the Schlong" Schlongini, who is the coolest kid in school. He along with many others get killed by Mr. Pumpkinhead which is played by detective (Baker).
In the end the detective dresses up as the Lawnmower Killer because no one is taking the threat seriously so he decides to teach them all a lesson. It all started exactly 13 years ago, when Mary Graves' older sister was murdered on Halloween prom night by a power-mowing maniac. Since then, Mary has experienced horror, sexual frustration, even psychoanalysis, but she still sees little lawnmowers everywhere. But tonight will be different. Tonight, at the new Halloween Prom, all the questions of the past 13 years will be answered as the pumpkin headed killer has returned. But hot on their trail is an obsessed cop (Joe Don Baker) who won't allow history to repeat itself.
The film borders on the ridiculous at times when Baker's family, all black eat cake at the dinner table and the slices of cake they enjoy are the size of a dinner plate. Baker also fills his suitcase (which has a tap on it) with coffee and later terminates Harry Vice (Vice principal) who is in charge of the vice. Harry Vice likes to "clamp on down," on student slackers but he ends up having his head clamped on down in a vice courtesy of Baker.
