Homer wakes up from a blackout only to discover that Marge and the kids have left him; and using a variety of methods, he probes his memory to unravel the mystery.

Homer wakes up one morning only to find himself outdoors and covered with snow. He has no recollection of what happened the night before, but his hangover is a sure sign he got drunk. Homer makes his way home, figuring he’ll slip into bed and pretend nothing happened. When he enters the house, however, his family is nowhere to be found. Hopelessly confused, Homer makes his way to Moe’s bar, where Moe reveals that Homer drank a “Forget-Me-Shot” the night before. The drink is so potent that it wipes out a person’s memory (the last 24 hours of it). Homer begins to worry that he did something awful during that time. Wiggum explains that there was a domestic disturbance at the Simpson house the night before. The scene shifts to the images and people populating Homer’s memory. Memory Wiggum asks Memory Marge how she got a black eye. Memory Marge claims she walked into a door. Homer discovers that Flanders phoned the police after hearing a commotion at the house. Homer fears that he struck Marge during a drunken argument.

Grampa claims he was at the house during the incident, but Homer soon discovers that his father is telling a fib to get attention. Desperate for answers, Homer turns to Professor Frink, who hooks him up with a device that will allow him to explore his memories. When the device is turned on, Homer finds himself with his Memory Family practicing their ski moves on a hill. The scene shifts to the Simpson house, where Homer observes as Memory Marge and Memory Homer have a conversation. Memory Homer returns home early from his bowling game only to discover Marge on the couch with a strange man whose face he can’t see (it’s obscured by a champagne bottle). Homer turns to Memory Bart and Memory Lisa for help. The kids jump off the dining room table, causing the “frame” in Homer’s memory to jerk around. Eventually the identity of the stranger on the couch is revealed: it’s Duffman. Convinced that Marge has run off with another man, Homer makes his way to a bridge, and prepares to jump.

Patty and Selma happen along, and encourage Homer to jump. When he takes too long, Patty gives him a shove. As Homer plummets to his certain death, his life flashes before his eyes. In flashback he sees Marge and Duffman on the living room couch. It turns out that Marge had been planning a surprise party for Homer in congratulations for completing his community service. Homer is overjoyed; Duffman was in the house as part of the celebration. As Marge takes a bottle of champagne out of Homer’s hand, she accidentally hits herself in the eye, leaving a bruise. The scene shifts back to Homer as he continues to plummet to his death. Instead Homer lands on an air-filled moon-bounce atop the deck of the Duff Party Boat. Carl congratulates Homer on pulling off his mission: making the surprise party a surprise again. It turns out that Homer drank another Forget-Me-Shot to forget that he found out about the party. A short time later others at the party fill in the blanks, explaining why things happened the way they did.