18 Beware My Cheating Bart

During a day out in the mall, Homer decides to dump Milhouse and Bart at a children's movie so he can eat at the food court. The boys run into the bullies (who are there to see an R-rated remake of a Hong Kong horror film called "Crawlspace") and Bart is forced to chaperone Jimbo Jones' girlfriend Shauna while she sees a Jennifer Aniston movie. Both of them leave shortly after seeing the only part of the movie that appeals to Shauna (the man's ass) and they hang out in the mall. Bart covers for Shauna when she shoplifts and when they escape from an incompetent mall cop, Shauna says that Bart is pretty cool and shows her appreciation by flashing her breasts in front of him, leaving him both traumatized and smitten with her. Both decide to enter a romantic relationship behind Jimbo's back, but he figures out what's going on soon afterwards. Both attempt to hide from a vengeful Jimbo at Comic Book Guy's store, while the bully decides to stake out Bart's home with help from an oblivious Marge, leaving Bart to come home and face Jimbo's wrath. Shauna breaks up with both of them after some good advice from Lisa, and Bart receives his punishment (being held upside down from his treehouse to have the "fear of God put into him") from Jimbo.

Meanwhile, Homer is persuaded to buy a state-of-the-art treadmill from a crafty salesman. When Lisa shows Homer that he can access television shows wirelessly, he takes advantage of the machine and develops an obsession with watching an old television show called Stranded, instead of working out. Eventually Marge, in a fit of rage, gives away all the spoilers of the episodes Homer has not watched yet. He is initially furious at Marge and threatens to divorce her for ruining the episode, but a romantic evening planned by her resolves matters.