Cartman goes to the eye doctor and has to wear a huge pair of glasses. He is especially angry at the fact that the doctor constantly makes fun of his weight. At lunchtime, Cartman shows up in front of Stan, Kyle and Kenny, since he never misses lunch. The boys go in to get their lunch, but instead of Chef, there is a skinny white guy called Mr. Derp, a funny-but-illiterate man who irritates the boys, with the exception of Cartman.
After school, the boys go to Chef's house and discover he is engaged to a woman named Veronica. They discover Chef has quit his job and has become overall duller and lamer of a person to them. Veronica even plays a song for the boys, which they all hate. The next day, the boys visit Chef at his new job. Chef tells Cartman he should get laser corrective surgery for his eyes when Cartman asks for advice. Chef then tells the boys he'll meet them after school to play ball, but fails to show up to the anger of the boys, who realize something is very wrong.
After class, the boys ask Mr. Garrison for advice. He tells them the woman is probably a Succubus, a demon sent from Hell to suck the life out of men and that he just "screws them and leaves them". The boys tell Garrison that he is quite good at advice, which he is happy to hear. Mr. Hat tells him he "isn't fooling anybody" by pretending to like women, implying that he is gay.
The boys go to tell Chef that Veronica is a succubus, Cartman is then dragged away by his mom to go for his laser corrective surgery. When they arrive at Chef's house they are greeted by Chef's Parents who announce he's getting married. They spend the rest of the episode ranting on about their alleged encounters with the Loch Ness Monster. Unfortunately for the boys, Chef is too busy to talk.
Cartman has to stay in bed after the eye doctor ruined his corrective surgery. Veronica comes to see him and shows him that she baked him a pie. Stan, Kyle and Kenny say they know what she is, but Veronica convinces them that she's not a monster. However, her face suddenly transforms to that of demon and she says they cannot stop her from marrying Chef the next day before leaving. Terrified, the boys realize they have to stop Veronica at all costs. At the party before the wedding the boys tell everyone that Veronica is a succubus which makes her cry. Chef chases the boys out angrily.
The boys begin to research the "succubus" and how to stop them; they discover that to stop her they must sing her song backwards. They figure out her song is "The Morning After" which she constantly sings. The boys learn the lyrics backwards and prepare for the wedding.
At the service, they stay calm until the wedding vows, where they tell Cartman to play the tape of the song's music backwards, but it's delayed from Cartman's lack of sleep. Veronica transforms into her demonic form and begins to destroy the church, scaring off most of the attendees. Unfortunately, Cartman's tape recorder jams and when Kenny tries to fix it, the Succubus jumps on Kenny, crushing him. Fortunately, the tape resumes and the boys finish the song, defeating the Succubus and sending her back to the depths of Hell. They apologize to Chef but upon seeing what he almost did, he thanks the boys. Everybody leaves content, but Cartman, still disoriented, asks, "Is Kenny OK?"
Later at the eye doctor's, Cartman gets the doctor to give him an eye transplant, giving him the frozen head of Kenny.