After having two weeks off of school after their teacher Ms. Choksondik's death, the boys finally return to class with Mr. Mackey as their new teacher. Over their break Bebe developed breasts. Though they are small (she said she originally thought they were mosquito bites), they are noticed by the boys in her class who start to think she is really smart and cool, without realizing why. They invite her to throw rocks at cars after school, much to the annoyance of Wendy Testaburger who has never been asked to hang out with Stan Marsh and his friends before.
The boys in the class start to fight and bicker with one another over Bebe, and the attention and praise they give her make Wendy and her other friends jealous and they start calling her a slut. Bebe talks with her mom about what happening, and she tells her it's just a part of growing up, and that boys use to think she was dumb then one day they thought; "I was really smart, so I guess being smart just runs in the family."
Meanwhile, Eric Cartman, Stan, Kyle Broflovski, and Tweek decide they want to make room in their group for Bebe so that she can join. They end up kicking Cartman out of the group to replace him with Bebe, to which Cartman replies; "That's fine! That's fine! Fuck you Kyle! Fuck you Stan! Fuck you Tweek! Bebe, you're still cool." Cartman invites Bebe to his house though to play and when the rest of the boys from class show up they all start to fight over Bebe, causing their minds to reset to a primitive state (they can only shout "A-TA!"; meaning breasts) with Stan (using a bone as a club) being victorious.
Bebe locks herself up in her house with the boys waiting outside for her. She expresses doubt to her mom about whether or not she really is smart and cool, and if the only reason the boys treat her so nice is because of her breasts. Her mom denies it, saying their whole family is genetically smart. Bebe tests that by asking her mother what 6×8 is, to which she replies "Oh sweetie, those are two completely different numbers."
She goes to Hells Pass Hospital to get breast reduction surgery, but is denied because performing breast reduction surgery on an eight-year-old girl is unethical to the doctor, though he would have no problem making them bigger. That night while Bebe is sleeping her breasts start conspiring on how to destroy the town, but Bebe wakes up and hears them and decides to not let her breasts take over her life. Wendy takes a trip to the hospital as well, but to get breast implants.
The next day at school Bebe starts wearing a box, hiding her breasts, and the boys snap out of their ape states and wonder why she isn't as cool as she use to be. Stan finally realizes that it was her boobs that were making them think she was smart and cool, which is why they had been fighting with each other. The boys make up and decide to never let boobs come between then again. Wendy then arrives with adult-sized breast implants, but they all laugh and make fun of her instead of praising them.