"Treehouse of Horror XXIII" is a Halloween-themed episode from the twenty-fourth season of the animated comedy series The Simpsons. It was first broadcast in the United States on the Fox Network on October 7, 2012, the most days before Halloween that any "Treehouse of Horror" episode has had its first airing so far.
In common with all other Halloween episodes of The Simpsons, the program is made up of three self-contained stories; "The Greatest Story Ever Holed", "Un-Normal Activity" and "Bart and Homer's Excellent Adventure". The second segment parodies the 2007 movie Paranormal Activity and its sequels. The title of the third segment references the 1989 time travel comedy movie Bill and Ted's Excellent Adventure but the plot more closely resembles that of the 1985 movie Back to the Future.
The opening sequence begins in Central America many centuries ago. It features ancient Mayan versions of Homer and Marge Simpson and other recurring characters from the series. The Mayan Homer discovers that the reason that he was being fattened up was to serve as a human sacrifice, intended to prevent the end of the world. The Mayan Marge tricks a guard (a Mayan version of Moe the bartender) into sacrificing himself instead. The Mayan Professor Frink explains that because the wrong person was sacrificed the world will come to an end after the thirteenth baktun finishes in the year 2012.
The scene changes to the year 2012. Three stone Mayan gods, initially mistaken for trick-or-treaters by Homer, are seen attacking Springfield and several well known landmarks from around the world. The Earth begins to split apart. The Mayan gods fly off as the Earth explodes, leaving the words "Treehouse of Horror XXIII" in blood-like lettering in its place.
"The Greatest Story Ever Holed"
Lisa Simpson has persuaded the people of Springfield to build a particle accelerator, although most of them would have preferred to have spent the money on a baseball stadium. The people of the town gather to watch as the machine is activated but are disappointed when nothing exciting happens. After they have left, two particles collide and form a miniature black hole, which floats off and is found by Lisa. After ithe black hole sucks in two boys, Lisa takes it home to prevent it from causing any more harm. The hole is stored in the Simpsons' basement. Lisa warns the rest of her family that if they put anything in the black hole it will get bigger but they ignore her. Her father Homer even opens a business, charging people to throw their garbage into the hole. The black hole becomes enormous and sucks in everything and everyone in Springfield, except for the baby Maggie Simpson whose pacifier falls into the black hole, plugs it up and saves her. The people of Springfield find themselves in another world where aliens worship the trash that the black hole has sent them.
Strange things are happening in the Simpsons' home. Homer Simpson sets up cameras around the house to investigate. It is eventually revealed that the disturbances are being caused by a demon (who resembles the Simpsons' recurring character Moe the bartender). Thirty years earlier, out of boredom, Marge Simpson's sisters Patty and Selma performed a Satanic ritual which conjured up the demon. Marge begged the demon not to carry off her sisters, as it had threatened to do. The demon agreed but on the condition that it would return in thirty years to take Marge's favorite child. Much to Lisa's surprise, the favorite child in question is not her but the baby Maggie. The demon says that it will leave Maggie alone, if Homer agrees to have sex with it and another demon. Homer is reluctant at first but soon proves to be kinkier than the demons.
"Bart and Homer's Excellent Adventure"
Angry that a 1974 Radioactive Man comic book with a cover price of twenty-five cents costs $200 at Springfield's comic book store, Bart Simpson uses Professor Frink's time machine to travel back in time and buy the comic book new. While he is in 1974, Bart encounters teenage versions of his father Homer and mother Marge. He tells the teenage Marge never to marry Homer.
Back in the present, Bart finds that he is now the son of Marge and Artie Ziff and that his family is wealthy and powerful.
The teenage Homer from 1974 has stowed away in the time machine. He finds his present day counterpart and they devise a plan to win Marge's affection. They summon various different versions of Homer Simpson from different historical periods. They all join together to fight Artie Ziff. Despite the fact that he is massively outnumbered, Artie manaages to defeat all of them. However, Marge takes pity on the defeated Homers and they end up winning her heart.