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 violently until Homer intervenes and orders them to stop fighting. He throws a burning log at them, but misses and hits Grampa, though he complains "I'm still cold". Homer gets Bart and Lisa rolled up in the rug and starts to "beat the lumps". A gun-wielding Marge intervenes and says that she does not approve of Homer's parenting techniques, and shoots him. Homer's blood splatters on a nearby wall, and spells "Treehouse of Horror XIV". Meanwhile, from their spaceship, the two aliens Kang and Kodos criticize the Simpson family for airing a Halloween special in November, as they are already set up for Christmas.
The Grim Reaper enters the Simpson house attempting to take Bart but the family goes on a Benny Hill-style chase to elude him. Death eventually manages to pin Bart's shirt to the wall with its scythe. As Death is about to sentence Bart to an eternity of pain, Homer kills him with a bowling ball in revenge for killing Snowball I and President John F. Kennedy. The Simpsons find that no one can die since Death is dead. The scene cuts to two examples of a world where no one can die: Frankie the Squealer (last seen in "Insane Clown Poppy") is repeatedly but unsuccessfully gunned down by the Springfield Mafia, much to their frustration, and Moe hanging himself unsuccessfully from the ceiling. On trash day, Marge tells Homer to take the dead Death to the curb. Homer does, but puts on Death's robe, inadvertently turning himself into the new Grim Reaper. At first, he refuses to reap souls, but when the cloak begins to give him a wedgie, he complies.
He kills many people who are on God's list (and some who are not) until he is asked to kill Marge. Homer does not want to kill his wife (or himself, an alternative he is given but quickly rejects), and pleads with God that he wants to get out of the job after leading Him to believe that he killed Marge. God agrees, but he finds that Homer tricked him by substituting Patty's body (which God initially mistakes for Selma's) for Marge's. The annoyed deity tries to punish Homer with a deadly sunbeam but gives up after a chase, proclaiming that he is "too old and too rich". Marge thanks Homer by giving him extra pork chops. Homer then jokes that he will make sure to not kill Marge every week from now on.
In a parody of Frankenstein, Homer gets a call from the Royal Swedish Academy of Sciences telling him that he is the winner of the Nobel Prize; however, Lisa learns that it is actually for Professor Frink. Frink is depressed because his father, an adventurer, had a falling out with him and died from a shark bite before they could reconcile. Frink, who kept the corpse frozen, reanimates his father. Unfortunately the revived man decides to steal body parts to improve himself. Eventually, Lisa convinces Frink Sr. to stop when he realizes he is causing his son anguish.
At the awards ceremony in Stockholm, Frink Sr. tries to make amends with his son for his recent behavior; however, he goes on another rampage through the audience, killing many and taking their brains. Frink Jr. manages to stop his father by kicking him in the crotch, killing him. Before dying, Frink Sr. is proud of his son for standing up to him, however he is able to hold on to his father's soul, which talks to him from a box.
In a parody of the Twilight Zone episode, "A Kind of a Stopwatch", Bart and Milhouse get a stopwatch through an advertisement in an old comic book that actually allows them to stop time. Realizing the power behind the watch, they set off to prank Springfieldians with impunity, such as depantsing Principal Skinner. They have a blast using the watch to terrorize the town, but they are eventually outsmarted by Mayor Quimby, who laid ultraviolet powder on the floor at the town meeting where they committed their most recent joke. Upon discovering the perpetrators, an angry mob goes after Bart and Milhouse. Just as the mob is about to converge on them, the boys use the watch to once again freeze time. The watch then breaks, leaving the two in a frozen world.
For a time, they have some fun with the entire world (such as giving the Pope a wedgie and punching Oscar de la Hoya in the stomach) but soon become bored. They find a watch repair manual, but it takes the two 15 years to repair the device. Just before they re-activate the watch, and realizing that they need a scapegoat to avoid the mob's anger, they place Martin in the middle of the mob that was just about to maul them; he is viciously attacked. Later, Lisa makes light of the fact that Bart is much older, and asks to play with the watch. She finds a secondary function that changes reality, altering the family in many ways (including causing them to switch genders, and become bobble-heads, TV Guides and the Fantastic Four). Homer has her stop when the family, now normal with Bart at 10 years old again, is playing with hula hoops.