Still jittery from a nightmare in which the school bus crashes in a thunderstorm, Bart boards the bus with Lisa during a storm. While riding on the bus, he sees a demonic gremlin ripping wires and metal from the side of the vehicle. When the other children look out the window, they see nothing. Bart watches as the monster loosens nuts from the bus's rear tire. In desperation, he pulls the emergency exit handle, hangs out the rear window, and shoots the monster with a flare.

After closing a deal to buy the Springfield Blood Bank, Mr. Burns invites the Simpsons to his castle in Pennsylvania. Lisa suspects that Burns is a vampire. At the castle, Burns bites Bart. Later that night, Lisa is awakened by Bart and his vampire friends, who float to her window. Homer and Marge are convinced that their son is one of the undead. They learn from Lisa that the only way to save Bart is to kill the head vampire, Mr. Burns. Although Homer drives a steak through his boss's heart, Bart remains a vampire. To her horror, Lisa discovers that her mother is really the head vampire.