The Simpson family becomes helplessly stuck in traffic while returning from a ski vacation. To pass the time, Bart, Lisa and Maggie spend hours playing the repetitive and noisy game "Bonk-It", much to Marge and Homer's annoyance. Homer loses his patience and throws the toy out the window, where it is crushed by passing vehicles. By a twist of fate, another father throws his children's Bonk-It out of a car window, and it lands in the hands of the Simpson children. Eventually the batteries run out, but Bart plugs the toy in to the car's cigarette lighter, causing it to play even faster. His patience long gone, Homer smashes the Bonk-It with his foot, but it becomes lodged under the brake pedal. He loses control of the vehicle, hits a deer reminiscent of Bambi and ends up on a frozen lake, where a mysterious person drags them out. When the family wakes up, they discover that the mysterious person who saved them was Cletus. Cletus tells Homer about moonshine, and invites him to taste the latest batch. Homer impresses Cletus and his hillbilly friends with his moonshine-tasting skills and is invited to be the judge of a moonshine competition.
Meanwhile, Bart and Cletus's sons play with a box of grenades that Cletus's wife Brandine, a former soldier, had brought back from Iraq, and Lisa plays hide and seek with Cletus's daughters. They do not find her, and Lisa gets lost in the woods. Trying to find her way back, she encounters three girls who are Wiccans, practicing their full moon Esbat. Lisa is initially skeptical of their ability to cast spells, but becomes interested after she happens to mention in the witches' Circle that she wishes she did not have to hand in her unfinished art project, and her wish comes true when Miss Hoover is taken ill with a stomach virus. The girls ask Lisa to join their coven and she accepts, but on the night of Lisa's induction, Chief Wiggum turns up after being tipped off by Ned Flanders and arrests the three girls on suspicion of witchcraft. Outside the courtroom, the girls say a chant, asking their goddess to 'show their persecutors that they are blind'. Many of the townspeople then suddenly become blind, and blame the three girls, who are then put on trial. When the judge dismisses the case, the townspeople decide to take the law into their own hands, and wish to drown the girls in an impromptu witch trial. Lisa, however, proves that the real culprits behind the town's temporary blindness are Homer and his friends, who threw their moonshine in to the town's reservoir after thinking that they were about to be arrested by the police. The girls are released, and Homer entertains himself by using the witch-dunking chair to binge drink the moonshine water, but falls off the chair into the river.
The episode ends with Lisa ice-skating on the frozen river to the song "Season of the Witch" while her skates carve a hole in the ice that frees Homer.