The simmering rivalry between Springfield and its neighboring town, Shelbyville, heats up when a group of kids from Shelbyville steal Springfield's prized lemon tree. It's up the youngest Springfieldians to cross over the town line and reclaim what is theirs. During the mission to get the tree, Bart develops a particularly intense rivalry with Shelby, the leader of the Shelbyville posse. The two square off and the Springfield kids, with the help of their parents and a stolen RV, manage to get the tree back.