Golden child Lisa Simpson finds she's starting to tarnish just a little when a new girl, Allison Taylor, moves to Springfield. Allison is smart, pretty, a great saxophone player and a crack diorama builder. Lisa tries to befriend her new rival, but she's consumed with envy and competitiveness, especially as Dioramarama, the annual diorama competition, approaches.
Turning to Bart for help, Lisa devises a way to humiliate Allison by replacing her expertly crafted diorama of Edgar Allen Poe's The Tell-Tale Heart with an actual, rotting cow's heart. Lisa feels pangs of regret at the last minute and backs out of the prank, only to see Allison lose the contest to Ralph Wiggum, who simply displayed Star Wars action figures in their original boxes.