"Summer of 4 Ft. 2" is the twenty-fifth episode of Season 7.
In the hopes of making friends on the latest family vacation, Lisa packs an empty suitcase, determined to leave her 'nerdy' self behind.
It is the end of another school year at Springfield Elementary School. While Bart and Milhouse discuss their plans for the summer vacation, Lisa is taking care of the distribution of yearbooks. However, even with her academic track record and accolades in the yearbook (she edited the entire thing after Mr. Estes died), she becomes very disappointed when nobody wants to sign her yearbook. Later that day, Flanders makes a deal with Homer to watch over his beach house in Little Pwagmattasquarmsettport while he serves jury duty. The Simpson family head out to the beach house, with Marge suggesting that Bart could bring Milhouse and Lisa bring a friend, too (only that Lisa has no friends).
Seeing this as a chance for a new beginning, Lisa abandons her old, nerdy image, and tries to develop a new kind of person, including "forgetting" to bring a swimsuit (Homer also forgot to bring a swimsuit, although he "improvised" by wearing the welcome mat over his otherwise bare crotch, which is also implied to have gotten himself arrested when he flashed himself). She gets a cool new look at the beach, and finds some skateboarding friends: Erin, Dean, Rick and Ben. Trying her best to fit in, she humiliates Bart by telling her new friends that he is a nerd.
Because of their vacationing there during Independence Day week, Homer plans to buy illegal fireworks at the Li'l Valu-Mart to celebrate the holiday. Because of this, Homer, to cover up the fact that he is buying illegal fireworks, also buys some porno magazines, a box of condoms, pantie shields, and one, eventually two disposable enemas. After making sure everyone else was out of the store, the clerk then directs him to a secret closet containing lots of fireworks, and Homer buys the M-320 firework at his recommendation. Upon returning home, Marge, not realizing the other items he bought were a cover, told Homer to "count her out" of his plans for the evening. Homer and Bart later attempt to launch the M-320, but that was derailed when Bart does not have a lighter or even matches. Homer's disappointment ended quickly when he chooses to light the fuse with the stove. Unfortunately, he burns off far too much of the wick, forcing him to play "hot potato" with the soon-to-detonate firework, eventually throwing it into the fridge, only to change his mind after realizing the beer was still inside, then grabbing it and then eventually throwing it in the dishwasher, and closes it and ducks just as it explodes. Homer sighs in relief, although the explosion severely damages the adjoining sink, resulting in it spewing up sewage and oil and flooding the floor with it. Homer then walks off whistling with his hands behind his back. Marge eventually has to clean up the mess as Bart as complains about Lisa's newfound friends.
Bart becomes furiously jealous of the attention Lisa is getting (since she had lied about him and even stole some of his catchphrases), and attempts to ruin her friendships by showing them Lisa's accolades in her yearbook. Saddened at this event, Lisa runs off in tears.
The next day, Lisa confronts Bart for humiliating her. He tries to defend himself by saying that it is important to be herself, but Lisa shows how sore she is with him. Milhouse defends her by calling him out for the action. He points out how hurt she was in not having friends at the school because Bart kept taking them from Lisa by being an attention whore. He starts to feel guilty over it, but tries to defend himself. Milhouse mentions that Lisa's newfound friends really hates Bart for the whole thing and thinks of him as an egotistical jerk. The family attends the carnival, where Bart and Lisa continue to battle over the previous night's events. Finally having had too much of her brother's torment, Lisa dejectedly leaves believing that he will never let her shed her nerdy persona and walks back to the beach house. Bart watches this and realizes he went too far in hurting her. Milhouse once again reprimands him for going to far and intends to tell on him to Marge about this unless he does one good deed in his life. Once she arrives, she discovers her friends have decorated the family car with seashells. When Lisa asks why they would do such a thing for her, they let her know that they aren't bothered by what they saw in her yearbook. To them, she is still a great person. Homer walks out and sees the shells on the car, and exclaims "Sweet merciful crap! My car!" out of shock, horror and fury at the new decorations.
As the family leaves the next day in their car, with various seabirds also attacking the car due to the presence of shells, Bart gives Lisa's yearbook back to her. He reveals to her that before they left he showed it to her new friends, who signed little messages inside. Lisa smiles and thanks Bart for the kind gesture, as the Simpsons and Milhouse head home. Marge berates Homer for his actions and insists that he should have gone to the car wash and cleaned off the shells before they left for home.