Buffy is still hurting because Parker dumped her after a night together. In a daydream during one of Professor Walsh's classes (pointedly, about the role of the id in Freudian psychology) she saves Parker's life and he swears to do anything to get her back. A dialogue with Willow later shows how much Buffy is not over him yet.
In the real world, Xander gets a job as a bartender with a fake ID, and has to endure the insults from students. He gets to test his empathy skills with none other than Buffy who then proceeds to get drunk on "Black Frost" beer with four college boys. Oz and Willow are in The Bronze together, but he feels a strange connection to the pretty singer Veruca when she gets on the stage with her band Shy.
The next morning, Willow not only has to cope with Veruca having called her a "groupie", but also with Buffy, who seems to be suffering from "Black Frost." That evening when Buffy drinks herself further and further into idiocy we get a glimpse why: somebody has a chemical lab set up and is putting more into the beer than just malt. Xander finally sends Buffy home. When her four drinking buddies turn into violent Neanderthals, he finds out that the owner of the pub has been brewing the beer as revenge for 20 years of college kids taunting him. While the boys escape to the streets of Sunnydale, Xander gets Giles to help. They find Buffy drawing cave paintings on her dorm wall saying "Parker bad." Giles and Xander are unable to keep Buffy in her room when she gets a craving for more beer.
Meanwhile, Willow confronts Parker with what she says he has done to Buffy. When he turns his charm on her, she reveals she has been playing along with a rant about how primitive men are, just when the four Neanderthal students burst into the room. They knock Willow and Parker unconscious and start a fire that rapidly burns out of control. Xander catches up with Buffy and when they see smoke from the Neanderthals' fire, they rush to help. Though afraid of the flames and unable to figure out how to use an extinguisher, Buffy saves Willow and Parker. In the end, Parker thanks Buffy for saving his life, and apologizes just the way she had dreamt - just to get knocked unconscious by Buffy's club. The neanderthal students become subsequently locked in a van.