The opening sequence features the Simpson family as candy bars on Halloween, trying to avoid getting eaten.
The Exor-Sis: Maggie gets possessed by an evil demon called Pazuzu.
Coralisa: Lisa, along with Snowball V, discover a creepy/perfect version of her family in an alternate universe.
MMM... Homer: Homer cannibalizes himself after he runs out of food while Marge and the kids are away from home.
In a CGI short known as "The Sweets Hereafter", it is Halloween night in Springfield as trick or treating is going on, and a bowl of candy is in front of a house. Suddenly, the candy comes to life, where Barterfinger is afraid that someone might take him, but Marge Bar comforts him and tells him not to worry, because he is always the last one to be taken. Oh Homer! tells Barterfinger that even the boxes of stale raisins get taken before him, but mistakes Barterfinger's name for "Butterfinger".
As Nelson's Crunch and Kirkish Taffy get taken, Apple Lisa discovers that no trick or treaters ever wants the apple, because they must be frightened that there is a razor blade in it. Barterfinger understands(ironically) that is the reason, and Marge Bar tells Apple Lisa that maybe she will be dipped in caramel, which makes Apple Lisa bored at the fact. Suddenly, Shauna reaches for the candy, but Oh Homer! avoids getting taken by letting Senior Mints get taken instead, and asks Oh Homer! where is he going. Oh Homer! tells Senior Mints that he is going to heaven.
As Senior Mints gets taken by Shauna, Oh Homer! tells Senior Mints that change is always hard. Shauna then opens up the box of Senior Mints and starts to eat them down her throat, to which Senior Mints freaks out and even gets scared about the cigarette breath that she has.
The next day, as the owners of the house are taking down their Halloween decorations, the bowl of candy is now almost empty and now the Simpson family are the only ones left in the bowl. One of the tenants grabs the bowl, and while walking with it to a high shelf, Marge Bar tells the rest of her family that they pulled through the night, much to their surprise.
After the bowl is placed onto a higher shelf, a chocolate easter bunny tells the family that they are on a high shelf where people will forget about them forever, just like himself. As the chocolate easter bunny sadly asks himself why won't people take him, Oh Homer! comforts him, takes a piece of the bunny's ears, and eats it. However, Marge Bar tells Oh Homer! not to do it, but Oh Homer! tells her to not be silly, because chocolate doesn't feel anything, so he takes another piece of the bunny, much to the bunny's horror. Apple Lisa worriedly tells Oh Homer! that she can't listen to the bunny's agony, so Oh Homer! eats the bunny's mouth off in order for it to be silent.
Eventually, the Simpsons choose to eat the entire chocolate easter bunny for themselves. The camera then pans to the wall, where it has the words "The Simpsons Easter Special" (written with Peeps, jelly beans and other easter treats). But, because of the Simpsons eating the chocolate bunny, the chocolate splatters onto the wall, thus covering up the words, followed by some dark chocolate to spell out "Treehouse of Horror XXVIII" over the milk chocolate.
In a pre-Christian temple site in northern Iraq (a parody of the opening scene of The Exorcist), a Pazuzu statue is dug up and sent through Amazon to the Simpson home due to Homer accidentally ordering it, thinking that it was pizza. After Homer, who is possessed, sings the Pazuzu Lullaby to Maggie, the statue is placed across from Maggie on her crib, and right after Homer leaves, Pazuzu possesses Maggie.
Meanwhile, Marge and Homer are having their cocktail party downstairs, but Marge notices the possessed Maggie making her presence. She proceeds to kill a complaining Helen Lovejoy before locking everyone indoors, and then killing Dr. Hibbert while revealing that he is cheating on his wife. Later, Ned Flanders tells the Simpsons that Maggie needs an exorcism, but when he tries to hold her down, he gets killed by Maggie.
Homer and Marge succeed in tying the possessed Maggie down, but then she starts to turn her head 360 degrees. Eventually, an Irish priest arrives, and, after testing how powerful Pazuzu truly is, performs the exorcism that purges the demon from Maggie, but Pazuzu ends up possessing Bart, which he fearfully regrets, declaring that Bart has the evilest soul he has ever seen.
Bart tells Pazuzu to grow him some horns, which Pazuzu does. Homer, however, sees that the horns are nubs, not horns, to which Pazuzu grows the horns even longer that they impale through Homer's nose. Uncomfortable, Homer says that at least the horns will get him out of jury duty, but later, Homer is eventually in jury with a dismembered horn still through his nose, to which he shouts, "D'oh!"
In a parody of Coraline, Maggie has still got a touch of Pazuzu while starting to violently vomit all over the dinner table. In Lisa's room, Snowball V takes her through a secret tunnel that brings her to another version of the family, with buttons instead of eyes on their faces. While the alternate family are like a dream, Lisa runs back to her world in terror when she learns they want to sew buttons on her eyes so she can remain with them forever. Lisa reconsiders the alternate family's offer after Homer had killed a snake with Lisa's saxophone.
A few days later, the family finally realizes Lisa is missing with Homer accepting it and saying Maggie that gets Lisa's room and clothes, while Bart gets her homework. Upon hearing this, Bart escapes through the door and is accepted in the alternate reality. After Marge follows after her children, Homer follows suit and a meeting with the alternate family results with him killing the alternate Bart while alternate Homer injures himself on a pair of scissors trying to avenge him. This infuriates alternate Marge as she transforms into an eight-legged spider-like creature to attack Homer, who decides to take advantage of the situation to benefit himself: bringing the surviving members of the alternate family home with his alternate counterpart attending parent-teacher meetings while alternate Marge does the chores and guards the house. Lisa accepts this outcome, claiming that it could have been much worse.
Homer remains home while the rest of the family goes on a vacation with Patty and Selma. Homer gets comfortable, but ends up eating his food supplies, ending up with only vegetables before finding a frozen hot dog. Losing the hot dog to Santa's Little Helper in the process, Homer accidentally cuts his finger off while grilling with his severed digit cooked as he eats it. He discovers how tasty it is, losing interest in other food when invited by Ned for lunch, and starts to cannibalize himself by cooking parts of his body before his family come back. When Marge discovered Homer's self-cannibalism, she takes him to a addiction counselor for help, but Mario Batali, in search for new ingredients, convinces a despondent Homer to cook his remaining body parts as ingredients sold at Chez Homer and several restaurants across Springfield. In Heaven, Homer comments to Jesus of how he shares people eating parts of his body with him.
Preview Evil Comes To Springfield Season 29 Ep. 4 THE SIMPSONS
Homer Is Possessed By The Pazuzu Statue Season 29 Ep. 4 THE SIMPSONS
Maggie Throws Up At The Table Season 29 Ep. 4 THE SIMPSONS
Homer Cooks A Meal Using His Own Recipe Season 29 Ep. 4 THE SIMPSONS