“Marge, as a trained marriage counselor, this is the first instance where I've ever told one partner that they were 100% right. It's all his fault. I'm willing to put that on a certificate you can frame.”
Marge and Homer host a dinner party, and Homer gets drunk and makes an oaf of himself. Angry and embarrassed, Marge signs the two of them up for a marriage retreat. When Homer learns the retreat is being held at a popular fishing spot, he tries to bail out of the retreat to go fishing. Meanwhile, Grampa babysits Bart and Lisa, who trick the old man into letting them do whatever they want—including throwing their own party and smoking cigars.
Marge and Homer throw a dinner party. Homer gets drunk and humiliates himself by telling off total strangers, pulling a very juvenile (and probably medically dangerous) practical joke on Dr. Hibbert involving a fly in an ice-cube, dancing while wearing a lampshade as a hat, ogling Maude Flanders' cleavage and generally making an oaf of himself. Homer then passes out on the living room floor and sleeps until morning (Hibbert also suggests to Marge that, if she wants Homer to live through the night, that she roll him onto his stomach). The next day, in church, Marge enrolls the two of them in a weekend retreat of marriage counseling hosted by Reverend Lovejoy and Helen Lovejoy. When Marge hires a babysitter for the weekend, the sitter takes one look at Bart and runs away screaming, as she had been emotionally scarred by watching Bart when he was a baby. Marge ends up recruiting Grampa as a last-minute replacement to babysit for the weekend.
Homer finds out that the retreat will be held at Catfish Lake and plans to spend some time fishing, even though Marge tells him that the weekend will be spent resolving their differences and there won't be any time for fishing. Even so, Homer sneaks his fishing gear in with the luggage. Before they leave, Marge gives Grampa a list of numbers in case accidents happen, and secretly gives Lisa a number to call if Grampa falls in the tub. On the way to the retreat, Homer learns of the legendary catfish, General Sherman, and vows to catch the elusive fish.
Meanwhile, at home, Bart and Lisa decide to take advantage of being left with Grampa, with Bart creating a phony list of what foods they can and cannot have. This leads to a shopping trip where Bart smokes a cigar; Grampa gets candy, ice cream and other items for the kids; and Bart makes Grampa chauffer them to Krusty Burger and then to Noiseland Video Arcade.
During the first meeting at the marriage retreat, each couple is asked to explain the faults of the other person. When it is Marge's turn, her list is so long that she talks for several hours, and Reverend Lovejoy has to cancel plans for a luau. The next morning. Homer gets up at 5:00 am to sneak away and go fishing, but Marge wakes up and catches him. Marge is angry that Homer would choose fishing over their marriage, but the message is at first lost on Homer, who visualizes Marge turning into a catfish. Homer asks if he can take a walk instead, and Marge agrees. On the dock, Homer finds an abandoned fishing pole, picks it up, and gets yanked off the pier into a small rowboat and onto the lake. It appears that the rod has hooked the legendary catfish, General Sherman. From the cabin window, Marge sees Homer on the lake, and assumes that he has ignored her again.
Back at home, Bart and Lisa throw a party that ends with the house in a total mess. Watching Grampa cry, and fearing that he will get in trouble, Bart and Lisa start to feel remorse for taking advantage of Grampa, and they frantically work to clean the house up before Homer and Marge return. However, unbeknownst to them, Grampa secretly chuckles while they clean.
Marge attends the marriage workshops alone while Homer is still attempting to catch the fish. Finally he wrestles it into the boat, and after it stops moving, he returns to the dock, triumphantly singing, "I am the Champion." He finds Marge waiting for him, and she tells him their marriage is in trouble if he values a fish more than her. To prove that he loves Marge more, he lets the fish go (despite having battled it for several hours), Marge forgives him, and they return home to a clean house. Grampa admits he fooled Bart and Lisa into obedience by pretending to cry ("I can turn it on like a faucet!"), and the entire Simpson family realizes how clever he is.
Back at Catfish Lake, General Sherman still swims free, but the story of how Homer nearly caught him is added to the tale of the legendary fish, as told by the bait shop clerk.