Cartman seeks to rid the world of hippies once and for all.
Eric Cartman shows up at the doorstep of an elderly neighbor dressed in full pest control gear, telling her she may have an infestation of hippies. According to him, the number of hippies residing in South Park has been on the rise and Cartman, an avid hater of hippies, is determined to stop them. He finds "stoner hippies" in the attic and a drum circle in the backyard, and proceeds to round them up and lock them in his basement, where he has imprisoned dozens more hippies.
Meanwhile, Stan Marsh, Kyle Broflovski, and Kenny McCormick are asking passers-by to buy magazines to support the children of South Park, and come across a group of "college know-it-all hippies", who tell the kids that they have been tricked into selling themselves out to the corporations, who wish to get rich off the kids and rule the world. Infuriated by this claim, the boys adopt the hippies' ideology and want to know how they can stop the corporations. The hippies suggest hosting a week-long music festival, where they will gather together, and change the world through the power of music. The boys misguidedly tag along and become hippies themselves.
Meanwhile, Cartman informs the City Council of the hippie infestation, claiming that a hippie music festival is imminent and that such an event will allow the hippies to consume the entire town. The council and the Mayor do not take him seriously and have him kicked out. Cartman discovers that his three friends have joined the hippies and proceeds to mace them all in the city square. Suddenly, Officer Barbrady pulls up and arrests Cartman for illegally imprisoning sixty-three hippies in his basement. Cartman doesn't recognize his crime, insisting that the hippies are a threat to the town. Mayor McDaniels shows up at the jail and when Cartman reveals that there is an upcoming music festival, the Mayor says that she knows and that she signed the permit, as she hoped it would boost their economy. Cartman is infuriated, claiming that the hippies don't have money and that the Mayor has doomed South Park.
The hippie music festival commences, attracting thousands of hippies nationwide, who spend the entire event listening to music and getting high on joints and acid. Cartman's three friends are confused, as the hippies have not done anything meaningful for the world as they claimed they would. Asking the hippies for details about the plan to change the world, the boys realize that the hippies' idea of a perfect world is exactly like the one we have now. The boys try to explain this, but one of the hippies says that the boys wouldn't understand since they haven't been to college yet. Randy is angry that Stan is at the festival, stating that the hippies don't stand for anything like in the old days, when he and Sharon were hippies. Realizing that hippies back in their day were just as bad as today's hippies, Randy rushes to save Stan, only to collapse from the suffocating stench of the hippies' joints.
The festival gets out of control and soon, over half a million hippies reside in South Park, declaring it the Hippie capital of the world. The townspeople panic as the hippie population grows. Ashamed of what she has done, the Mayor puts a gun to her head and shoots herself in an act of suicide. Desperate, the townsfolk apologize to Cartman for not listening to his warnings, and beg him to get rid of the hippies. He refuses, even when they bribe him with a cake. However, he agrees to do it if he can get the new Tonka remote-controlled bulldozer, and if Kyle is not allowed to play with it and must watch Cartman do so. The townsfolk agree and Cartman makes plans to drill through the hippie crowd using a drilling vehicle. He will drive to the stage and insert a Slayer CD into the stereos, as hippies cannot stand heavy metal, forcing them to disperse. However, he needs a crew to man the vehicle, a scientist, an engineer and a black man to willingly sacrifice himself if things go wrong. Randy and Mrs. Stotch agree, so does an unwilling Chef.
The crew depart on their mission and say their farewells to their families, realizing that their mission could be suicidal. The townsfolk coordinate the mission from downtown, led by Mayor McDaniels, who by some miracle survived her attempted suicide. Cartman's crew drill through the crowd, killing hundreds of hippies in the process. Meanwhile, Stan has had enough of the hippies getting high and listening to gay music, and tells them that they have done nothing to change the world for the better. They, however, fail to grasp Stan's proclamations and say that they must play more tunes to change the world. Disgusted and ready to abandon the music festival, the other boys realize they are trapped due to the growing crowd behind them. Meanwhile, the drill overheats from all the hippies and Cartman forces Chef to "sacrifice" himself to the crowd, but not before activating the drill's emergency boosters. The Mayor suggests nuking the town, but the townspeople protest. Cartman's crew get the drill working and they storm the stage, killing the band in the process.
Cartman then proceeds to place the Slayer CD into the stereos, upsetting the hippies due to the song's angry mood, and they all leave the city. The boys are freed and Randy reunites with Stan. Chef also survives his ordeal in the hippie crowd. Cartman then brandishes a knife and threatens Kyle, who insists that he is not a hippie anymore. Cartman, however, does not wish to kill him, saying he has bigger plans for him.
Cartman gets his new Tonka RC bulldozer and Kyle is forced to watch him play with it. Cartman offers to give it to Kyle, but says he can't and continues to play while Kyle looks on with annoyance.