The Munster clan heads to a local wax museum that proudly displays wax replicas of the family themselves. As the museum prepares to close, a scientist activates a controller that stirs the figures to life—though these are not true people, they are robots. The robots of Herman Munster Fred Gwynne and Grandpa Al Lewis rampage, scaring citizens and slipping away with a few stolen items. The next morning, the police arrive at the family home to arrest the pair for theft, and they’re put behind bars. Yet no jail can hold a Munster for long, and the duo makes a daring escape, stealing the police chief’s car and driving back to the wax museum after hours in a bid to clear their names.
When the scientist triggers the robots again, Herman Munster Fred Gwynne and Grandpa Al Lewis deactivate their doppelgängers and slip into the laboratory unobserved. There they encounter Dr. Dustin Diablo, a schemer whose plan unfolds in a hidden plot—an encounter led by the cunning Sid Caesar. The Munsters are then whisked away by a moving van and dumped outside a busy pizzeria, where they witness a money exchange between the scientist and a mysterious owner. The van departs, forcing the family to improvise a return trip home and bide their time.
Back at home, Marilyn Munster, played by Jo McDonnell, convinces Glenn Boyle, a rookie detective and the son of the police chief, to help the family clear their names. The trio narrates what they know about a hidden laboratory, but when Glenn heads to search the wax museum, the scene has shifted—robots and the laboratory have vanished, much to the frustration of his father, Police Chief Harry Boyle Herb Voland.
With the mystery deepening, Herman and Grandpa improvise again, disguising themselves as waitresses to infiltrate the pizzeria where the owner and his accomplice depart. They tail the two back to the wax museum, and once there, they slip back into the guise of the robots and overhear Dr. Diablo’s plan to seize the jewels of a pharaoh mummy on display during Halloween. Grandpa hatches a bold scheme: use a life rejuvenation serum on the mummy to bring him back to life and use him to capture the gang. The catch is the serum is locked away back in Transylvania.
The Munsters manage a perilous journey by plane to Grandpa’s old laboratory, where Grandpa’s old assistant Igor (brought back to life by a serum injection) appears, just before he dies again. Grandpa injects the serum into Igor, restoring him to a younger, more capable state. This detour buys time, and the family returns home just before Halloween, only to discover Marilyn and Glenn have gone to the wax museum and haven’t returned. A rescue mission unfolds as Cousin Phantom of the Opera Bob Hastings and the entourage reach the museum, where Marilyn, Glenn, and Herman have been captured inside a shatterproof container.
A triumphant note from Cousin Phantom shatters the container, freeing the trio and reuniting them with Grandpa upon arrival at the museum. In the frenetic finale, Grandpa administers the rejuvenation serum to the mummy, while Marilyn steals the robot controller, rendering the robotic guards useless. Dr. Diablo makes a last-ditch attempt to seize the jewels, but the mummy—now fully animated—greets him instead, drawing the police to the scene and helping vindicate Glenn. In a twist revealed at the end, it becomes clear that Herman Munster is the mummy, a result of Grandpa giving the real mummy too much serum, leaving him aged down to the surprising state of a three-year-old.
Throughout this zany Halloween caper, the Munster family’s love and loyalty shine as they navigate deception, science, and a city-wide misunderstanding, all while keeping their signature warmth and comic timing intact. The film blends family dynamics with outlandish gadgetry, a dash of crime caper intrigue, and the timeless charm of the Munsters’ unique, homegrown humor.
