After dropping Shelley off at Cartman's home, the Marshes and Stan are off to a party at the home of School Counsellor Mr. Mackey. Stan is upset that he has to go and becomes even more angered when he is locked in a room with nerdy "Melvin" classmates that he does not like: Pip, Butters, and Dougie.
While Stan refuses to play with the other children, Butters discovers women's clothing and the three begin to play Charlie's Angels. Butters plays Kelly Garrett (Jaclyn Smith), Dougie plays Jill Monroe (Farrah Fawcett), and Pip plays Sabrina Duncan (Kate Jackson). Stan, unenthusiastic to participate, plays Bosley as he gives the trio missions to keep them occupied. Stan tells them to find a way to get out of the basement, and find a comfortable place with a TV. They do this which surprises Stan, and when they get up stairs, Stan tells them to get chocolate chip cookies and a television. After they do this, Stan tells them that there are no more missions because he has everything he wanted.
Upstairs, Mr. Mackey gives the Broflovskis and Marshes a tour of his home and leads them out to the hot tub, which was installed just recently. The wives leave Randy and Gerald outside in the hot tub, who declare the present evening to be a night of experimenting. The two talk about threesomes and engage in mutual masturbation. This leads to awkwardness after Randy questions his sexuality.
The ATF thinks that the party inside is a suicide cult that at the start of the meteor shower will kill themselves and the children inside. The ATF panics and attempts every possible solution to prevent what might happen. They resort to playing what they see as terrible music only to cut to Mr. Mackey playing the same music on his own stereo system, to the delight of the partygoers. The ATF then procedes to kill anyone that leaves the house and does not obey orders (although they end up shooting people who do nothing wrong). Soon, Stan and the Melvins discover what is happening outside. They try to talk to the ATF, but they are all shot at like everyone else who left the house. Stan and the Melvins then make a tape and send it to the ATF outside. The ATF realize their mistake, but not before destroying every house except the one in which the party is taking place (though it is implied that their leader knew all along). The ATF then flees after their leader suddenly claims that the whole operation was a training exercise.
Inside, Randy is extremely uncomfortable being around Gerald, who is concerned about Randy's behavior. When Randy is forced to admit to the entire party that he and Gerald engaged in group masturbation, he is relieved upon discovering that he's not the only one to have masturbated in front of a person of the same sex. Outside, the boys rejoice their triumph of saving the day and Stan realizes that the Melvins are just normal kids like him. All is forgotten, however, when Kyle returns from Jewbilee camp and Stan goes back to his old ways, telling Kyle that he had to "spend the evening with these friggin' Melvins".