At Arnold's, Chachi comes out of the kitchen with a bunch of food orders. He puts each dish in front of the people whom he thought ordered them. When he leaves, they all switch plates. Al comes out of the kitchen and bumps into Joanie. He cleans the table where Joanie is going to sit and goes back into the kitchen. Chachi tells Al he's taking his break and sits down with Joanie. Joanie tells Chachi to remind his mother that dinner is at 7:00 tomorrow. He says he can't go and has to work. She says he's not invited. Her parents want to see Chachi's mother without him to show her that they like her for herself. Joanie says her parents were thrilled that Chachi's mother was free for the night. Chachi says she's always free. Fonzie comes in and puts a large, rolled up poster on Joanie and Chachi's table. Joanie has to leave to get a turkey for dinner the next night when Louisa comes over. Fonzie says he's free until 9:00, but Joanie says he's not invited. After she leaves, he asks Chachi what she just said to him. Chachi says it's one of those adult dinners. Fonzie opens the poster and says that Bobby made him a chart that includes the birthdays of all of his women. Chachi asks what happens when four birthdays come up on the same day and shows him one of the squares. Fonzie says he can't have four birthday girls in the same night because he only has one set of hats. He goes into his office to straighten it out. Al comes over to Chachi and tells him to lock up. He says he's going home to soak his comb, change the cheese in the mousetrap, and update his diary (all he has to do is add ditto marks). Chachi asks Al if he'd like to take out his mother. Al gets all excited. Chachi tells him just to pop over there and that it's no big thing.
At the Cunningham house, Howard and Potsie come in. Howard explains to Potsie that when they lock up the hardware store, he goes to his house, and Potsie goes to his. They don't see each other until the next working day. Potsie says he's supposed to work until 6:00 and doesn't want to cheat Howard. Howard tells Potsie to cheat him. He says there's nothing more to do than have dinner. Potsie takes this as an invite and sits down at the table. Howard goes into the kitchen (where Marion and Joanie are) and tells Marion that Potsie is driving him crazy. He says he hangs around him all day. Marion tells Howard that Potsie likes him and mentions that he was never close to his own father. He tells her that tonight is the night Louisa is coming over, and Potsie just invited himself to dinner. Marion says she'll handle it. She goes into the living room with the intention of uninviting Potsie, but she can't after he tells his stories about not getting anything to eat when he was growing up.
At Arnold's, Chachi comes out of the kitchen as Al comes in from outside. He's wearing his pajamas and bath robe and tells Clarence to bring him all of the food that he hasn't eaten the last two years while he was on his diet. Chachi goes over to Al and asks what's going on. He says he's been watching television all day. He says he's sick at heart and that Chachi's mother ripped it up into little pieces. Chachi says he heard his mother come in late last night and says Al and her must have had a good time. Al says she had a good time but not with him. Al says he went to Chachi's place wearing a new suit and driving a rented car. He brought her flowers and candy and asked her to go out with him. Some guy came in, and the two of them went out together on a date. Chachi consoles him. Chachi is shocked to find out that his mother has a boyfriend. He says he's going to the Cunninghams' to get to the bottom of this.
Chachi shows up at the house where Howard, Marion, Potsie, Joanie, and Louisa are eating dinner. Chachi says that he guesses it's okay for a son to find out about his mother's affairs on the street. Louisa is sorry that Chachi found out about Walter the way he did but says it was a perfectly respectable date. Chachi says that, by the way the story was told to him, the guy must be a low-life deadbeat. Louisa says they'll talk about it at home, but Chachi says he isn't going home and probably never will. He storms out. Louisa apologizes to everyone for the embarrassment. She says her situation with Chachi is very difficult. Potsie says that, as a psychology major, he understands her situation. He says she's been avoiding personal relationships for years for fear of upsetting the family emotional balance. She says he's exactly right.
In Fonzie's office, Chachi tells Fonzie that he made a jerk of himself in front of everyone: Joanie, her parents, and Potsie. Fonzie is surprised to learn that Potsie was invited when he was not. Chachi tells Fonzie to forget about Potsie for a minute. Fonzie doesn't think he can, but he'll try. Chachi tells Fonzie that his mother is dating a guy. Fonzie already knows and says he set them up. He says Walter is a doctor he met while he was working on his car. Fonzie brings up Potsie again. Chachi asks Fonzie what he thinks they do on dates, and Fonzie says they do what adults do. Chachi says he hates Walter. Fonzie tells him to meet Walter before making any judgments.
At Dr. Walter Danzig's office, a pregnant woman comes out and says she can't wait until her baby is born. Chachi comes in saying he's "Chachi Smith" and is there for his 4:00 appointment. The receptionist asks where the patient is, and he says he is the patient. She says that she thinks he has the wrong place. He asks if he can see the doctor, and she tells him to go right in. Chachi introduces himself as "Chachi Smith." Dr. Danzig asks where the patient is, and Chachi says he is the patient. He hops on the table. Dr. Danzig suspects Chachi is not there on a medical matter and tells him that he's an obstetrician and that he delivers babies. He tells Chachi that he has bad news for him: he's not having one. Dr. Danzig asks if his name is Chachi Arcola. He says Chachi is not a very common name. He's been looking forward to meeting Chachi and asks why he lied about his name. Chachi says he came down there to check the doctor out. Dr. Danzig asks Chachi to give him a few minutes while he leaves to straighten the whole thing out.
Later, Louisa comes in saying that Walter said he was worried about him. She asks Chachi what he thinks of Walter, and he says he's a fairly decent guy. He still hates him. They argue briefly about what has happened the past few days. Louisa says she should have told Chachi about Walter right away, but she didn't want to make an unpleasant scene. She says the important thing is that she likes Walter and says she's entitled to her own life. Chachi says he wants her to be happy. He likes Walter, but he's not his father. He says it's not going to be easy for him to get used to this situation. She asks him to try, and he apologizes. She squeezes his face and offers to make him ravioli.
At Arnold's, Fonzie and Dottie celebrate her birthday. He says she'll look strange with her party hat on, so he takes it back. They (Fonzie, Al, and Chachi) send her off and get ready for the next girl, Samantha. She comes in and they sing "Happy Birthday" to her.
Songs in this episode:
"The Locomotion" (instrumental) by Little Eva (1962)
"My Boyfriend's Back" (instrumental) by The Angels (1963)
"Georgia On My Mind" by Ray Charles (1960)
"That's Life" (instrumental) by Frank Sinatra (1966)