During winter Homer wakes up in a pile of snow and does not remember the events of the previous day, commenting that he must have drunk heavily the night before. Homer goes home and finds his family absent and Santa's Little Helper attacks him. Homer travels to Moe's, where Moe informs him that he was there the previous night and wanted to forget an unpleasant memory. Moe explains he gave Homer a "Forget-Me-Shot", which wiped out the last 24 hours of his memory; the ingredients of which include Jägermeister, sloe gin, triple and quadruple sec, gunk from a dog's eye, Absolut Pickle, the red stripe from Aquafresh toothpaste and the venom of the Louisiana loboto-moth then stirred with a home pregnancy test. Chief Wiggum tells Homer that there was a domestic disturbance at his house last night, which was reported by Ned Flanders. Homer instantly receives a flashback to the night before showing Wiggum questioning Marge about a black eye she had received, to which Marge nervously replies that she walked into a door.
A still confused Homer goes home, where a picture of Marge causes a flashback of her pleading Homer to stop, and then rubbing her eye in pain. Horrified, Homer goes to Grampa Simpson for help. Grampa tells Homer about Professor Frink's new machine that helps people sort through their memories. With the help of this technology, Homer sees himself walking in on Marge and Duffman in an allegedly compromising position. In the flashback, Marge tells Homer that she did not want him to find out about it, and Homer assumes that Marge was cheating on him and that Homer beat his wife as payback.
Homer now considers his life to be worthless and decides to commit suicide by jumping off a bridge. He begins to reconsider, but is pushed off by his "guardian angels," Patty and Selma. While falling, Homer's life flashes before his eyes. He then sees the full memory of the preceding night: Marge was planning a surprise party for Homer finishing his community service, and did not want Homer to find out about it. Duffman, who was hired by Marge to entertain at the party, brings out a bottle of Duff Champagne. Overjoyed, Homer tries to open the bottle, while Marge pleads with Homer to stop, as she wants to save it for the party. The cork flies off and hits Marge in the eye. The flashback ends and, instead of falling to his death, Homer lands on a moonbounce, which is at the surprise party on board a ship.
When Homer asks Marge why she lied to Chief Wiggum, she claims that she did not want him at the party, because he would bring Sarah Wiggum, whom Marge does not like. Lenny and Carl appear and cause a flashback which shows Homer telling his bar buddies that he felt very guilty for finding out about the party that Marge worked so hard on. When Moe offers the Forget-Me-Shot (which Moe spat in), Homer predicts exactly what is going to happen, and tells Lenny to make sure there is a moon bounce at the party. Finally, it is revealed that the dog attacked Homer because he does not take care of him.