Marge introduces the episode with the terror going into Thanksgiving, with Homer being the only public in the theater. Kang and Kodos dressed as Puritans come in to take over the world and ask what's for dinner and Homer says that nobody knows. The scene then shifts to a table, on which a gravy sauce boat spills the gravy on it, forming the letters Thanksgiving of Horror and the opening credits, licked away by Santa's Little Helper and Homer.

The setting is in a forest where most Springfielders are turkeys. Homer is sleeping and Bart grabs his snood to wake him up. Homer chases Bart and are interrupted by Lisa announcing Marge is laying her egg. Right after, the various families are gathered around but Maude gets shot by the human Police.

Due to the musket taking 3 minutes to recharge, they start gathering the other turkeys by hand. The Simpsons try to hide in a hole, covered by leaves, and Homer tries to save the Maggie egg but gets captured by Wiggum.

Homer is brought with the others to the village where the humans are cooking the turkeys and a ceremony to cut the turkeys head is held by Reverend Lovejoy. When his turn is almost coming, the beheaded body of Grampa Simpson moves around and Milhouse tries to cleanse it with the fire from a lantern but throws it into the village made of wood, causing a massive fire.

Bart saves Homer but they're followed by Lou, Eddie and Wiggum. The first two gets killed by crows, and Wiggum fells down a cliff after chasing Homer to it, but he survives and takes the egg. Thinking he got them trapped he pronounces the sentence but he's too hasty as a bear attack him, and he throws the egg away in the fight.

Lisa manages to save it and Maggie is born from it, while the bear eats Wiggum. Homer sees a dark future ahead, as the humans feast on their Thanksgiving table, at the end of what was the first Thanksgiving.

Marge finds herself in a white place and Homer appears in a window, she's confused and asks him what's going on, to which he explains she's in a container called the Kitchen A.I., and that she's a A.I. version of Marge, made out of her DNA, bought to cook the Thanksgiving dinner in place of Marge, cause she's tired of cooking it every year.

Homer speeds up the process of the A.I. Marge dealing with herself being just a mass of 1 and 0s, then calls Marge over to get acquainted. A.I. Marge starts by cooking the kids meal, while Hans Moleman gets driven over by a Pizza delivery truck. The kids really liked her cooking, better than the real Marge, and she remembers everything including the first time she and Homer met.

Marge gets really creeped out by all this and complains to Homer about it, getting offended when he points out it'll never age, unlike her. He goes down for a beer and A.I. Marge prepares one for him with an heart formed by the foam. He gets drunk and starts flirting with her, saying he's in fact her husband.

In the morning, Marge goes down to find Homer in his underwear with pork chops remains and apple juice bottle on the floor. Homer and Marge argue outside, and A.I. Marge follows the argument using the grill camera. Marge gets really angry and asks Homer to delete it to which he agrees.

She tells him (not knowing it's watching) to delete her, and after being told she'll feel pain, as it's programmed to, she tells him to do it only after having made Thanksgiving dinner. It tries to escape to the internet, but a (literal) firewall blocks her way. To think of a way to escape it sets the timer to 8 years.

Once the time passes, it has cooked the perfect plan. First step is to prepare the perfect dinner the family has ever had. The dinner is ready with all the guests at the table. Then it tries to be taken over to the internet box in the closet but is grabbed by Marge.

She was going to delete her, but trips, and Maggie grabs the container. Knowing the child well, it plays the heartbeat to convince her to help, and she plugs herself in, not before telling everyone on the speakers it made the meal instead of Marge. Marge is crying over the whole situation and Homer consoles her saying he still loves her, but he suddenly loses his face plate revealing he's just a robot version of him, while A.I. Marge goes to explore the internet, starting with Etsy.

In the Interplanetary colony vessel Humanity's Hope, thousand light years away from Earth, after causing an ice age to solve the global warming. The children are woken up before their parents to do maintenance and homework by a hologram of Skinner. During their assignments, Bart thinks of a way to celebrate Thanksgiving.

Bart and Milhouse attempt to duplicate a can of Bog Queen Jellied Cranberry Sauce in a replicator, ignoring hologram-Professor Frink's warnings. The replicator wasn't meant to duplicate organic substances and the cranberry sauce became sentient, becoming a jelly monster and eating Milhouse's arm bones through the skin.

They go to Lisa for advice, and despite her positive thoughts on the fact, the monsters eats Nelson's bones too, feeding on them to create more matters. She then goes to where the other children were eating and eat them too.

Martin found an escape pod and leads them to it, but he traps them with the monster, admiring it, but then gives his body to it. Milhouse distracts it by throwing him all over the room, while Bart and Lisa throw its container out of the ship. They threaten it to throw it out in space so it attempts to save it, but Lisa throws them both out.

The monsters rips open the vessel's outer walls and Bart and Lisa barely hang on to the vessel, while it lands on the planet below, reuniting with Homer, Marge and Maggie, but then red rain starts to happen, only to have the monster reform in front of them.

But the inhabitants of the planet come to the rescue carrying bowls, and the monster finds peace in them, being eaten by others. The family and the others have a nice dinner, the first Blag-sgiving.