"Summer of 4 Ft. 2" is the twenty-fifth and final 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 ideas for the summer vacation, Lisa is taking care of the distribution of yearbooks. As the bell rings Milhouse gets out and insults Mrs. Krabppel, and runs outside. However, Krabappel points out that it was 9 a.m, when the bell rang and she informs them Summer vacation begins at the end of the day, not the beginning. Milhouse was brought back inside by the policeman Lou, who tell them they have an inside man, with all the students staring angrily at Martin Prince who chuckles innocently. Even with her academic track record and accolades in the yearbook (she edited the entire thing after Mr. Estes died), Lisa becomes very disappointed when nobody wants to sign her yearbook. Bart on the other hand walks with autographs for and from everyone. 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 prepares to head for the beach house, with Marge suggesting that Bart could bring Milhouse and Lisa bring a friend, too (only that Lisa has no friends). While packing for the trip, Marge comes into Lisa's room and asks her mom why she has no friends, Marge says that she could be Lisa's friend. While Lisa does appreciate the offer, she tells her mother that she needs friends who are her age, in other words, she needs kid friends. Marge assures Lisa the best way to make friends is to be yourself.
Lisa decides to repack her bag by getting rid of her swim cap, nose plug and her microscope which she angrily questions. The next day the Simpsons and Milhouse head for the beach. When they arrive at the house, Marge sees a note from Ned saying he left a few notes around the house with instructions. When they come inside, the house is covered with sticky notes, which Marge remarks, "A few notes Ned?" 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 anything including 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). Marge, Lisa and Maggie go to the store to get some new clothes for her, unfortunately most of the clothes that Marge suggests are for little girls which Lisa's steering away from. She gets a cool new look at the beach, and after walking around finds some skateboarding friends: Erin, Dean, Rick and Ben. Trying her best to fit in, she tries skateboarding herself and humiliates Bart by telling her new friends that he is a nerd when he tries to show off to her friends to get in. Erin and her friends however don't let him in saying that he "tries too much," and even calls him Dennis the Menace. Angered and even jealous Bart leaves and blames Milhouse for not getting in. Later that night while Bart and Milhouse play a board game with Homer and Marge, Lisa goes for a walk on the beach with her friends and shares both her knowledge and love of nature, which Erin and the others begin to appreciate.
Because of their vacationing there during Independence Day week, Homer chooses to go buy some illegal fireworks at the Li'l Valu-Mart to celebrate the holiday. Because of this, Homer decides 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. At the beach house, Lisa and her friends are hanging out in the living room all discussing what they normally do on the Fourth of July. Lisa suggests a beach party which everyone supports. Upon returning to the cottage, 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 ends 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 that this is the worst 4th of July ever.
Bart becomes furiously jealous of the attention Lisa is getting (since she had lied about him and even stole some of his catchphrases) from Lisa's newfound friends, he tells Marge that they are supposed to be his friends and that Lisa "stole" them from him. With his jealousy getting stronger, he attempts to ruin her friendships by showing them Lisa's accolades in her yearbook. In the meantime, Erin gives Lisa a Friendship Bracelet making them her first real friends as a sign of her friendship she gives Erin a seashell necklace. While enjoying some fun on the beach, Bart ruins the entire moment by showing the 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. He starts to feel guilty over it, but tries to defend himself. 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. While walking home Lisa starts to think that she was never meant to have friends since being herself didn't work and being someone else didn't work either. Once she arrives at the house, 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, various seabirds attack the car due to the presence of shells. Marge, irritated by the seabirds pursuing the car, insists that Lisa's friends should have cleaned off the shells before gluing them on. Bart gives Lisa's yearbook back to her, he reveals to Lisa 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.