The Simpson family visits a home and garden show where they decide to purchase a hot tub. They spend hours soaking in the tub and become so relaxed that they forget to visit Abraham "Grampa" Simpson at a family event. Grampa angrily unplugs and destroys the hot tub, scolding them for ignoring him. Homer decides to make up for their neglect and decides to do something Grampa wants to do. Grampa reminisces about a pub in Dunkilderry, Ireland called O'Flanagan's, where he claims to have had the best night of his life many years ago. Homer decides to take Grampa there for one last drink. When the family arrives they realize Ireland has become a commercialized, hi-tech country of consumers and workaholics. The pub itself has run out of business as many of the patrons are now yuppies who have no interest in drinking. The pub owner Tom O'Flanagan is happy to have customers again. Homer and Grampa sit down at the pub and start drinking while Marge, Bart and Lisa visit various Irish landmarks. They visit the Giant's Causeway, Blarney Castle, the Guinness brewery and Dublin.
After a long night of drinking, Homer and Grampa awaken and discover that they bought the pub from Tom O'Flanagan during the previous night's binge, much to their shock and dismay. They rename the bar and try to continue running it but get no business and have to find a way to market their unwelcoming business. Homer gets help from Moe Szyslak, who suggests that they allow people to do illegal things in their pub. They find out that smoking is now banned from Irish pubs and Moe urges the Simpsons to turn it into a smokeasy. They do a roaring trade, but are closed down by the Irish authorities. As a punishment, Homer and Grampa are deported back to America and have to pay a small fine. Chief Wiggum arrives to bring them back to the U.S., but accidentally hits himself with his nightstick and then Maces and Tasers himself.