Lisa conducts a secret experiment for the Springfield Elementary School science fair to see who's smarter, Bart or a hamster. Meanwhile, Homer is forced to swear off beer after being arrested on a D.U.I. Bart realizes what Lisa is doing and ruins her plans for the science fair by winning first prize for his own, more sensational, hamster experiment. Homer manages to stay off of beer for an entire month and, instead of drinking to celebrate his sobriety, he decides to stay on the wagon and enjoy a bike ride with Marge.