Bart is seen walking around a room with paintings in light of Rod Serling's Night Gallery and tries to introduce the show but Marge and Maggie interrupt telling Bart to tell the viewers the show is scary but Bart ignores and we watch the first part.
Homer falls asleep at work, dreaming of donuts. When he wakes up to get one to eat, he finds out from Lenny and Carl that the remaining donuts have already been eaten. Homer then declares that he'd sell his soul for a donut, causing the Devil (in the form of Ned Flanders) to appear. After signing a contract, Homer is given his donut, with the provision that as soon as it's finished, the Devil will own his soul. However, Homer finds a loophole: if he doesn't finish the donut, he's safe. Homer openly mocks this loophole, to which the Devil promises that he will go to Hell eventually. One evening, Homer goes down to the kitchen, and without realizing it, eats the last of the donut. As expected, the Devil comes to take Homer's soul, but Lisa asks him to hold a trial, which the Devil agrees to. However, Homer must spend the day in Hell being severely tortured. Aside from being chopped into pieces, the Blue Demon in the Ironic Punishment Division laughingly plans to feed Homer all the donuts in the world (this plan backfires when Homer gleefully keeps eating, much to the confusion of the demon). Back on Earth, Marge already has the trial area set up and hires Lionel Hutz to defend Homer.
The Devil and Hutz barter on specific terms before the trial begins: The Devil agrees to Hutz's request for bathroom breaks, and Hutz agrees that the Devil can choose the jury. The Devil's jury includes Benedict Arnold, Lizzy Borden, Richard Nixon (still alive at the time), John Wilkes Booth, Blackbeard the Pirate, John Dillinger, and the 1976 Philadelphia Flyers. The Devil gives the evidence of the contract Homer signed, pledging his soul for a donut. Lionel Hutz counters with the definition of a contract according to the dictionary, stating it as something that is unbreakable. Realizing that he's put his foot in his mouth, Hutz asks to be excused to the bathroom. When he doesn't return immediately, Marge finds the bathroom window open and Hutz long gone.
As the judge prepares to sentence Homer, Marge shows the jury a photo album showing their wedding day, where Homer's eating of the whole wedding cake sent them to the emergency room. On the back of a photograph, it is revealed that in a statement of love to Marge, Homer pledged his soul to her. This causes the jury to declare Homer's deal with the Devil to be revoked. However, the Devil is not willing to let Homer best him. With a zap of his power, the Devil turns Homer's head into a donut.
The next morning, Homer can't stop eating parts of his head. As he decides to go to work, Lisa cautions him to stay home because standing outside the house are the Springfield Police Department, waiting to rip apart his donut-made head and enjoy it with their morning coffee.
Bart has a nightmare where the bus crashes and wakes up very paranoid. Bart and Lisa then get on the bus on one rainy morning with Principal Skinner on the bus. Lisa informs everyone that Bart is acting paranoid, and asks that they act nice to him, causing everyone to laugh at him instead. In the middle of the ride, Bart hears tapping on the window, but it is only Groundskeeper Willie, who says he had to put down his mule and needs a ride. Bart's nightmare then comes true when a gremlin is attacking the bus. Bart keeps trying to warn everyone, but every time Bart looks, the gremlin hides and it even causes Otto to destroy Hans Moleman's AMC Gremlin. Bart then becomes very annoying and it causes Skinner to close the window, and forces Bart to sit next to Üter, the German foreign exchange student. Bart eventually gets the emergency flares and throws one at the gremlin, knocking it off the bus, only to be picked up by Ned. After arriving safely to the school, everyone notices severe damage done to the outside of the bus. Bart stopped the gremlin from destroying the bus, but with no one as an alibi, he is declared insane for his behavior and is sent to the New Bedlam Insane Asylum for the rest of his life. On the way, Bart begins to relax at the thought of never having to worry about the gremlin. At that moment, the gremlin shows up at ambulance's back window and shows Bart Ned Flanders severed head, causing him to scream uncontrollably.
Bart brings us to the famous "Dogs Playing Poker" picture (Homer is frightened at this painting), explaining they had a story to go with it, but it was "far too intense". So they had to put a random story about vampires together.
The Simpsons are watching TV to find out a vampire has been attacking people and this convinces Lisa vampires are real, though Homer debunks her, despite a report following of Mr. Burns buying a blood bank. Burns has blood visible from his mouth which he quickly slurps up. The Simpsons are then invited to Mr. Burns' mansion for dinner in Pennsylvania. There it is obvious that Burns is a vampire (with Smithers acting as Renfield) but no one believes Lisa despite obvious evidence (Burns' unknowingly mentioning over the entrance intercom how the family will be "fresh victims for his ever-growing army of the undead", Burns' shadow moving on its own etc). Bart and Lisa find Mr. Burns' secret lair while cleaning themselves from spilling "punch" (really blood) on themselves, which can be easily accessed by staircase. The vampires in the lair awaken, causing the two to flee. Bart notices a "Super Happy Fun Slide" commenting "Maybe I shouldn't... But when am I going to be here again?", and pulls it, turning the stairs into a slide.
Bart slides right into the clutches of a vampire woman while the rest of undead surround him. He's then presented to Mr. Burns who suddenly arrives transforming from a bat and stands over Bart menacingly (despite not knowing his name: "Well if it isn't little.. um... boy.") before biting him in the neck. Lisa makes it back to her parents and warns them, but they don't believe her when Burns appears, blood on his very visible fangs, with a clearly bitten Bart, who drones in a zombie tone that nothing happened to him. Later that night at the Simpsons home, Bart, now a vampire, visits Lisa's window. Showing her that he's bitten and vamped some of the Springfield kids (Milhouse, Martin, Ralph and Jamie), with Lisa being next. He break through the window, pins her down and bears his fangs. Just as he about to bite her, Homer, hearing the noise bursts into the room stopping him. This quickly reveals to the family that he's a vampire while Bart changes into a bat and flees into the night. Lisa tells her parents the only way to get Bart back is to kill Mr. Burns. They sneak back into his castle and stake Burns in his coffin (though not before Burns briefly comes back to life and fires Homer).
The Simpsons are then eating dinner and Lisa finds out that her whole family are vampires and that Marge is the real head vampire. The family then swoop in on Lisa but they stop and sing.
The episode finished 17th in the ratings for the week of it aired, with a Nielsen rating of 14.5. It was the highest-rated show on the Fox network that week.