Krusty the Clown is informed that the Krusty Burger is the unhealthiest fast food in the world, so he decides that his namesake restaurant should serve the "Mother Nature Burger" which is entirely vegetarian. All of the townsfolk like the new burgers, but soon the entire town has food poisoning, traced to tainted barley which was grown in the neighboring town of Ogdenville. The ensuing boycott destroys the local barley industry and the residents of Ogdenville, who are descended from Norwegian settlers and portrayed as overly stereotypical, are forced to abandon their town (to Norwegian romantic composer Edvard Griegs mournful "Aase's Death", followed by a phrase from the Finlandia Hymn by his Finnish counterpart Jean Sibelius).
The displaced Ogdenvillians migrate to Springfield, whose residents are initially hospitable and hire them as day laborers. Homer hires several Ogdenvillians to fix his roof, Marge hires a nanny named Inga to care for Bart, Lisa and Maggie, and Selma finds love with Thorbjørn, a brawny blond who also seems to enjoy taunting Homer.
After being pressured by some Ogdenvillian kids, Bart shows off to them on his skateboard successfully until he hits a bus and dislocates his right arm. Marge and Homer rush Bart to the hospital and are furious when they have to wait for 6 hours, due to many Ogdenvillians being injured while working for Springfieldians. Marge and Homer take Bart home where Marge personally fixes Bart's arm. Homer then goes to Moe's Tavern, only to discover that Moe is now serving "Aquavit" and the bar is full of Ogdenvillians. Homer demands a mug of Aquavit and, unaware of its strong alcohol content, is instantly intoxicated. The next morning he arrives to work at the power plant drunk and is fired on the spot.
Mayor Joe Quimby calls a town meeting, where it is decided that the Springfield border should be closed to residents of Ogdenville. Chief Wiggum and fellow officer Lou are too lazy to control the border themselves, so they distribute guns and beer to a group of vigilantes, among them Homer, Lenny and Carl. After Homer asks the assembled crowd to suggest a name for themselves "that evokes America's proud history of citizens rising up to defend our way of life", Cletus suggests "The Klan" and "The Nazis" but this is eventually rejected in favor of the decidedly less offensive "The Star-Spangled Goofballs."
After several failed attempts to keep Ogdenvillians out of Springfield, the vigilantes decide to build a wall. At first, Marge believes the wall contradicts the values of tolerance that she taught their children, but changes her mind when Maggie utters the Germanic word "ja" (meaning "yes"). The residents of Springfield hire workers from Ogdenville to assist with the construction of the wall since they cannot build it themselves. As the building progresses, the residents of both communities discover that their similarities outweigh their differences. Once the wall is complete, the residents of Springfield realize that they miss their neighbors, so the Ogdenvillians come back through a door they built in the wall and the police arrives with music to start a party for all the people there, and the episode closes with a picture of the Norwegian flag.