Homer joins the "Springfield Preppers," an off-the-grid survivalist group whose leader (guest voice Tom Waits) has set up a top-secret retreat outside of town to prepare for the end of the world, but Marge grows skeptical of the group's alarmist shenanigans.
Homer and Marge take the kids to a kids' fun center, which disappoints Homer as he has to watch the kids. Some kids end up in a secret room where they are dressed in black suits and white shirts and told, “Welcome to the Mormon Church, America’s most respectable cult.” However, upon seeing that the other dads have abandoned their duties, he does so as well. When a child leaves the building, it triggers an automatic alarm that shuts down the entire facility. Marge and the mothers pass the time by telling each other stories of childbirth, but the fathers instantly turn on each other and fight savagely. Homer is traumatized, and on a routine trip to Moe's Tavern, he admits his doubt of civilization's ability to survive a worldwide catastrophe and meets a man named Lloyd, who reveals himself to be a survivalist "prepper". Lloyd introduces him to the world of survivalists, and Homer quickly adopts their ideals and methods, storing necessary equipment in the family basement.
Studying how to become a survivalist, he neglects his job at the Springfield Nuclear Power Plant, and as a result, an electromagnetic pulse blacks out all of the power in Springfield. When Mayor Quimby cannot find a solution to the problem, Homer is prompted to take his family to a base camp his fellow survivalists, who include Superintendent Chalmers, have set up. However, after an argument with Marge over their new lives, Homer begins to doubt the other survivalists when they refuse to share their stored equipment to the others in Springfield. Realizing that everyone else needs the equipment, he steals it all that night and flees back to Springfield with the family. The survivalists quickly catch on and gain pursuit. The Simpsons manage to make it back to Springfield, only to find that the townspeople have quickly gotten over the EMP burst and recovered as a society, much to Lloyd's dismay. Lisa tells everyone that a big lesson has been learned from all of this; meanwhile, a meteor carrying a horde of zombies approaches the Earth.