Herman is taking short walks at the park during the night, as a remedy to his stress and insomnia. When other walkers see him, they are scared, telling the police that a monster is free at the park, along with a dangerous thief.
Herman is invited to a reunion of his old army outfit but finds himself unable to fit into his old uniform. Lily will only allow him to go only if he goes on a diet. When Dr. Dudley tells him to loose a hundred pounds in a week, Herman resolves only to consume water and vitamins. Unfortunately, the last day of his diet coincides with Thanksgiving.
Herman's twin brother, Charlie, is visiting the family with a silly machine. Charlie claims that the machine can get uranium from the water sea. But Herman is very upset and uncomfortable with Charlie's visit.
Grandpa wants to marry again, because he's feeling lonely. He looks for a fiancée in a matrimonial agency. Herman is against it, but Grandpa gets fascinated with a woman, which will be a fraudulent lady from the agency.
After a midnight visit to the drive-in, Herman falls a sleep in the family's Cadillac (not the Munster's Koach). The car is promptly stolen to be used as a getaway car on a bank job. When Herman awakens, the thieves mistake him for their getaway driver, Big Louie.
Marilyn is sent home from college because her tuition has not been fully paid. Herman goes to talk to the dean, but is mistaken for basketball pro Moose Mallory and is tricked into signing up. When the real Moose and his hick father are sent home by the coach, they decide to take out their grievance on Herman Munster.
Herman has a new Ham radio and picks up two friends of Eddie playing Spacemen on their walkie talkies. Thinking Martians have landed, he and Grandpa go out searching for spaceships using the latter's radio direction finder.
Lilly won't feed, speak to or let Herman let into their bedroom after he comes home from an office party past midnight. After four days and nights of this, Marilyn and Grandpa separately encourage Lilly and Herman to see (the same) marriage councilor.
Lily wants to do something with her spare time and she finds a job as a model. Herman gets angry and jealous, because he believes that all the men will admire her. Using his magic potions, Grandpa turns into a woman, in order to help Herman in a plan to make Lily jealous.
When Herman buys ten acres of land in Happy Holliday Valley from a crooked magazine ad, the family is delighted to find it a complete wasteland. But the con artists want to get the land back when they can strike a deal to sell the area for use as a missile site. So, they decide to scare the Munsters off.
Eddie tells his friend Sandy Baylor that his father can beat Mr. Baylor at the Mockingbird Heights drag strip. Instead, Herman ends up losing the Munsters Koach on a bet. Determined to win it back, Grandpa constructs his own roadster, the Drag-u-la, to beat 'Leadfoot' Baylor at his own game and win back the family's beloved Koach.
Herman befriends a young boy named Galen Livingston Stewart. At first he has a hard time convincing his family that the boy is real. For Galen it proves even more difficult to prove to his parents he did not imagine 'Uncle Herman' and his family. The Stewarts even hire a German psychiatrist, Dr. Siegfried Leinbach, to examine their boy.