Bart, Lisa, and Homer duck into the mall movie theater after Bart and Lisa have a mishap at the new barber and have to avoid the school's camera club. Inside, Homer watches a movie about the end of the world as foretold in the Bible, leading Homer to do a little research and work out that the Apocalypse begins in one week. Nobody listens to him, until he makes a prediction that "the stars will fall to the Earth", which is exactly what happens when a celebrity-filled blimp crashes, and soon Homer has a pack of followers who join him for the end"- and then desert him when the end doesn't happen, and don't listen to him when he discovers a mistake in his calculations (he counted 12 people at the last supper, but forgot to count Jesus, making 13) - especially Moe, who sold his bar to a company that turned it into a sushi restaurant.
Marge attempts to give her annual haircuts to Bart and Lisa. However, they would prefer going to a children's barbershop labeled Da Buzz Club in an attempt to have cool haircuts for the new school year. She refuses to take them, claiming it's too expensive and the family could save more money by having her cut their hair for free with her templates. Homer takes Bart and Lisa to the mall anyway, partially because he plans to drop them off at Da Buzz Club for them to get their haircuts while he goes to a bakery to buy the newly baked cinnamon rolls. After they leave, a depressed Marge is forced to cut her own hair with her template. At the mall, Bart and Lisa's haircuts go horribly awry, partially due to Bart being distracted by a game he was playing and didn't tell the barber what he wanted that lead to him being bald. Angered by Lisa laughing at him, Bart shaves off a part of her hair held by one of the curlers and have a haircut fight. Once they're identified by some of their classmates, Bart and Lisa are forced to hide with Homer from school photographers from Springfield Elementary inside a movie theater to avoid being photographed and made a laughingstock by their classmates. The theater is showing a Christian movie called "Left Below". After watching the movie, Homer thinks that the Rapture is coming and gets frightened. After coming home, Marge is furious with the messy haircuts that Bart and Lisa inflicted on themselves and forces them to wear wigs from the spare clipping from her own haircut. Homer is concerned by a upcoming rapture. However Marge and Lisa reassure him which comforts him into thinking that it won't come.
As Homer is driving the very next day, he thinks he sees the Devil, which is a man in an advertising costume. This thought process is reinforced by "the Devil" saying "follow me...uhhh" which was actually the man telling Homer to follow him into the restaurant he was advertising. Homer then sees blood falling from the sky, which is actually from an injured whale being carried by a helicopter. Because of seeing those two things, Homer convinces himself that the Rapture is coming. He tries to estimate the time and date, by using methods which don't make sense, and it thinks it will come on the 18th May at 3:15 p.m, which is a week away.
Homer goes around Springfield, telling everyone about this, but they don't believe him. He then says that the stars are going to fall from the sky. This actually happens, as there is a blimp accident at the "Krusty's Celebrity Salute to Specials". This makes everyone believe Homer, thinking he has actually foreseen this event. His believers follow him to the Springfield Mesa awaiting the apocalypse. However, 3:15 soon passes and nothing happens. This annoys everyone in town, including Moe, who sold his Tavern to a Japanese Sushi bar. Homer, upset, goes home and throws away all the books on how to predict the future, but realizes that there was thirteen people at the Last Supper, not twelve (as he used this as a way of predicting the Apocalypse). This means that the Apocalypse will happen late at night on May 19; not in the afternoon on 18 May. Homer tries to convince his family to help him warn everyone again, but they don't believe him. Homer, alone, makes his way back to the Springfield Mesa and when the hour passes, he thinks nothing is going to happen again. However, the next moment, he is naked and floating through space.
Homer is in heaven with a tourguide, which gives him some clothes, much to Homer's dismay. They fly pass a few heaven houses, where Homer sees a waterslide which can't be used for another year due to Leprachaun labour. Homer is told by the tour guide that all his wishes will come true in heaven. Homer wishes that the tour guide's head explodes, and it does.
In his room, Homer asks to see his family on the big screen TV. The guide shows him on the flat screen what happened with his family and pointed out their fault in all of this. Because everyone refused to followed Homer to the mesa for his Rapture: his family and friends are in Hell being tormented by the Devil for eternity. Homer is aghast and wants to save them so he goes to see the Lord. The Lord refuses to help him because Earth is where Jesus suffered and tries to convince Homer to let it go. He refused and threatens the Lord, saying he has made a very big mistake in making a powerful enemy in Homer. Homer goes on a rampage around Heaven to change the Lord's mind, but gets stopped by security. The Lord then agrees to undo the Rapture and turns back time under one condition, Homer must never mentioned what happened here. He agrees and the Lord says "Deus ex machina". Homer wakes up from this dream at the Mesa and is reunited with his family. He goes to Moe's Tavern to find it has been restored, and that is Heaven to Homer.