Homer is arrested for drunk driving on his way homer from a Duff Brewery tour with Barney. His license is revoked and he is required to attend Alc-Anon meeting. Meanwhile, Bart pelts Pricipal Skinner with a tomato that Lisa has grown for her science fair project. For revenge, Lisa secretly conducts an experiment to determine who is smarter, a hamster or her brother. The hamster passes the tests, while Bart fails miserably. Arriving home from an Alc-Anon meeting, Homer agrees to Marge's suggestion that he stop drinking for a month.

Bart discovers Lisa's plan to humiliate him at the science fair. He steals her hamster and dresses him in a miniaviator suit for an experiment demonstrating that hamsters can fly airplanes. The judges award Bart's project first place.

Overcoming the temptation, Homer makes it through the month without drinking and rushes to Moe's for a beer. However, realizing what drinking has done to the bar regulars, Homer puts down his beer and goes for a bicycle ride with Marge instead.