Bart and Lisa, dressed as Charlie Brown and Lucy van Pelt from the Peanuts series discuss their Halloween treats, and Lisa claims that hers are better than Bart's. The two then fight until Homer intervenes and orders them to stop fighting. He throws an inflamed log at them, but misses and hits Grampa. Homer gets Bart and Lisa rolled up in the rug and "beats the lumps". A gun-wielding Marge intervenes and says that she does not approve of Homer's parenting techniques, she then shoots Homer, splattering his blood on the wall behind Homer (revealing the title). Meanwhile In their spaceship, high above the earth the two aliens Kang and Kodos mock the Simpson family for airing a Halloween episode in November, while they already have their Christmas decorations set up, then they fly off.
Death enters the Simpson house attempting to take Bart, but the family goes on a Benny Hill-style chase to elude him. However, Death eventually manages to pin Bart’s shirt to the wall with its scythe. But As the Grim Reaper sentences Bart to an eternity of pain, Homer kills him with a bowling ball,(in revenge for killing Snowball I and President John F. Kennedy), but when he does, he learns that nobody can die since the Grim Reaper is dead. The scene then cuts to two examples of a world where no one can die: Frankie the Squealer being shot by the Springfield Mafia and Moe hanging himself from the ceiling. On trash day, Marge tells Homer to take the dead Grim Reaper to the curb. Homer does, but puts on the robe, inadvertently turning himself into the new Grim Reaper. He kills many people on God’s list (and some who are not) until he is asked to kill Marge. Homer doesn’t want to kill his wife, and he tries to plead to God that he wants to get out of the job. Then Homer pulls a fast one on God by substituting Patty’s body for Marge. The annoyed deity tries to punish Homer with a (presumably lethal) sunbeam but Homer narrowly escapes on his motorcycle, prompting God to sigh "I’m too old and too rich for this." Meanwhile, at the house Marge gives Homer an extra pork chop for not killing her. Homer then mentions that he will not kill Marge, everyday from now on. In which, everyone laughs about it.
Homer gets a call telling him that he is the winner of the Nobel Prize; however, Lisa learns that it’s actually for Professor Frink. Frink is so excited that he decides to reanimate his father’s corpse in order to have him appear at the ceremony. Unfortunately, the corpse of Frink Sr. goes on a rampage stripping organ from others, including Ned Flanders' heart, Principal Skinner's spine (his mother isn't amused), Comic Book Guy's ass and Sideshow Mel's trademark hair. At the awards ceremony in Stockholm, Frink Sr. tries to make amends with his son for his recent behavior, but he goes another rampage through the audience, stealing brains of scientists and growing more and more intelligent. Frink Jr. manages to stop his father with a kick to the crotch, and he is able to hold on to his father's soul (which talks to him from a box).
Bart and Milhouse get a stopwatch through an ad in an old comic book magazine for 49 cents that actually allows them to stop time. They have a great blast pulling pranks on Springfieldians, such as depantsing Principal Skinner and stealing Homer's doughnuts. They almost get away with it, but they are outsmarted by Mayor Quimby. An angry mob goes after Bart and Milhouse. While they are on the run, Chief Wiggum shoots at them; they stop time and the watch breaks, causing Bart and Milhouse to be the only two people moving in a world where time has stopped. They soon take advantage of this and go on a world wide crime spree, kidnapping the Pope for wedgying, stealing whatever they want and just generally doing anything they wish. They soon become bored though and realize they need to fix the watch. Although the watch repair manual states that each lesson lasts about an hour, it takes the pair 15 years to get the watch fixed and for things to go back to normal. Once repaired, the pair position Martin Prince to take the blame, and he is killed when time returns. However, Lisa points out that Bart has become a grown man and has amassed vast riches. In the interest of being fair, Bart allows Lisa to use the watch. She then discovers a second button which interferes with reality, causing the Simpsons to undergo various changes such as becomimg bobble heads, having their torsos separate from their bodies on jetpacks, become T.V. Guides, have their sexes swapped, become the Fantastic 4, and finally start hula-hooping to "Rock Around the Clock", and Bart is restored back to his normal 10-year-old self.