On a research trip, Lisa is shocked to discover that Sideshow Bob is now the chief scientist at a massive chemical engineering company, but her fears are allayed as she becomes enamored with his likeminded appreciation of high-culture. Meanwhile, Marge's attempt to preach healthy sexual practices to a teen church group goes awry.

After Lisa's new pet guinea pig destroys the Simpsons' living room art, Marge falls in love with a beautiful painting at the Van Houten's yard sale, which Homer snaps up for 20 bucks. But, when Lisa reveals it's by a famous early 20th century painter and could be worth $100,000, Marge and Homer face a dilemma: split the money with the Van Houtens, or keep the cash as a "cushion" for their kids.