Stacy Hamilton (Jennifer Jason Leigh) is a 15-year-old high school sophomore who works in the Ridgemont Mall at Perry's pizza parlor with the seemingly more sexually experienced Linda Barrett (Phoebe Cates). Mark "Rat" Ratner (Brian Backer) also a sophomore, works in the mall as "assistant to the assistant manager" at the movie theater. His friend Mike Damone (Robert Romanus), who also hangs out at the mall scalping rock concert tickets, believes himself to be both worldly and wise in the ways of women.
Stacy's brother Brad (Judge Reinhold) is a semi-dorky senior but is relatively popular because he has his own car and is a low-grade supervisor at All-American Burger, a favorite after-school hang-out and a place that treats teen employees well. Brad is spending his final year in high school basking in the joy of becoming the unfettered owner of his blue 1960 Buick LeSabre ("the cruising vessel"), which has only six payments left, and obsessing over the best way to ease out of the long-time relationship with his girlfriend, Lisa, who also works at All-American Burger.
Surfer-type Jeff Spicoli (Sean Penn) is the resident stoner who begins the new school year tumbling out of a Volkswagen Microbus after hotboxing in the parking lot as the final attendance bell rings. Spicoli tries to come into the stern Mr. Hand's (Ray Walston) history class after the final bell, but Mr. Hand has locked the door. Spicoli knocks on the door but when Mr Hand sends him to principal's office, Spicoli calls him a "dick," thus beginning a vendetta between Mr. Hand and Spicoli that lasts throughout the movie.
The sexually curious Stacy initially hooks up with a much older home stereo salesman, Ron Johnson of Pacific Stereo in the mall. He provides her first sexual experiences. He dumps her a few months later, causing Stacy to wonder what was wrong with herself and seek other relationships.
In addition to his brief encounters with Stacy at the pizza parlor during his breaks at the movie theater, nerdy Mark Ratner ends up with Stacy as his lab partner in biology class. Ratner receives pointers from his friend Damone, the scalper. With prodding from Damone, "Rat" goes over to the pizza parlor one evening and asks for Stacy's phone number, saying he'll call her to ask her out on a date. Embarassed, but flattered, Stacy accepts Mark's offer of a date.
The date goes well despite Mark forgetting his wallet at home and the tape deck being stolen from his sister's car during their dinner at a local German restaurant. They go back to her house, where she comes on to him. Inexperienced with sex, he chickens out, leaving her there with nothing but a robe on. This leads Stacy to confide in Linda that she belives (mistakenly) that Mark does not love her.
Back at school, Spicoli continues to annoy Mr. Hand, including one episode in which Spicoli arranges for a pizza delivery in the middle of class by a less-than-thrilled "Pizza Guy" delivery man (Taylor Negron) only to have Mr. Hand take the pizza away and distribute it to his favored students.
Meanwhile, Brad loses his cherished job at All American Burger in a dispute with an unsatisfied customer in which his mean-spirited boss instantly fires him. Brad feels betrayed when all of his co-worker friends don't have the courage to stand up for him to their dictator of a boss out of fear of losing their jobs too. As a result, Brad never speaks to any of his friends ever again. Brad is forced to take a new job at "Captain Hook Fish and Chips," a Long John Silvers-styled fish restaurant. Employees are forced to wear pirate uniforms, and after being laughed at by a beautiful woman (Nancy Wilson) while on a delivery, Brad quits in disgust while tossing all the "Catch of the Day" boxes out into the street.
At a pep rally before the football game with Lincoln High, Brad meets up with his girlfriend Lisa. In a complete turnabout from his plans to go solo during the summer, Brad bares his troubled soul to Lisa, telling her that he needs her now more than ever. But Lisa dumps him, saying she wants to see other people before she heads to college, the perfect culmination to Brad's personal annihilation.
As Brad's life crumbles as he now has no friends or job, Stacy and Linda are sitting by the pool discussing men. Meanwhile, Damone convinces Mark to give it another shot with Stacy. Damone leads Mark to Stacy's house, where Damone crashes the girl chat. Brad comes home, dejected, and goes into the house. The teens all comment on how Brad is so depressed after losing his job at All America Burger. Brad heads for the bathroom and starts to masturbate as he fantasizes about Linda approaching him in her bikini and undoing her top (in a now near-legendary scene set to The Cars' song "Moving in Stereo"). Linda jumps into the pool and gets water in her ear. She makes her way to the bathroom for a Q-tip and is shocked as she catches Brad masturbating, which ruins the pool party.
Later that evening, Spicoli is seen drinking beer, smoking marijuana, and lost in his own world as he joyrides in a 1979 Chevrolet Camaro Z28 owned by Charles Jefferson (Forest Whitaker), an ill-tempered, hulking jock who is the star of the Ridgemont football team. The car is a gift from a grateful alumnus, and Jefferson's little brother, along for the ride, freaks out as an unconcerned Spicoli drives like a maniac through the crowded city streets. Spicoli eventually wrecks the car when he swerves to avoid an oncoming car, and crashes into a concrete wall. Spicoli promises to Jefferson's brother that he can fix it.
The next day at school, a large crowd gathers around the front entrance--where Jefferson's totaled car is covered in anti-Ridgemont graffiti. Spicoli has apparently made it look as if the rival high school, Lincoln High, destroyed it as a prank. Jefferson takes out his anger on the Lincoln football team that night, winning the game single handedly and sending Lincoln's quarterback out of the game on a stretcher.
Over the next several weeks, Stacy grows attracted to Mark's friend, Damone. Stacy meets Damone after school and Damone drives her home. Damone asks if Stacy has any iced tea and then he wants to go for a swim. She brings him into the changing booth near the pool. Instead of swimming, the two have clumsy, unsatisfying sex in the changing booth.
Later, Stacy tells Linda that she is pregnant. Stacy tells Damone and they decide that an abortion is the only solution. She asks Damone to pay for half the abortion ($150) and give her a ride to the clinic. Damone agrees. A little later, Damone and Ratner get into a fight over Stacy in the locker room after Ratner hears that Damone has been with Stacy and they cut ties with each other.
Damone has a hard time coming up with his half of the money to pay for the abortion. Damone desperately and unsuccessfully attempts to collect from past "clients" who owe him money. It is only then that Damone finally discovers how little power and popularity he has with the other teens. Ashamed, Damone does not show up to drive Stacy to the clinic and avoids her phone calls. Stacy catches a ride with Brad to a nearby bowling alley under the pretense that she is meeting some friends there. Brad sees Stacy leave the bowling alley and enter the clinic. After the procedure is finished, Brad is waiting for Stacy outside and talks to her about what happened, though Stacy will not tell him the identity of the father. Stacy's sibling bond grows with Brad when he shows a brotherly act of kindness by not pressing the issue. Linda, however, is not so charitable. After Stacy tells her of Damone's deception, Linda goes after Damone by scrawling "Prick" in spray paint on his car door and "Little Prick" in marker on his school locker.
Another month or two later, Stacy and Mark are fated to be together again when they go on a biology class field trip to observe an autopsy performed by their flaky biology teacher Mr. Vargas (Vincent Schiavelli). Spicoli tags along with the class (despite that he does not take biology) just for the excursion. When Mr. Vargas starts to rip organs from the corpse, Stacy feels sick and Mark helps her out of the procedure room. Stacy is grateful to Mark for staying with her and says he's "a nice guy."
School is coming to an end. Mr. Hand takes some revenge on Spicoli by visiting him at home on the night of the graduation dance and administering an impromptu American History lesson long enough to delay Spicoli until well after the prom has started. Surprisingly, Spicoli does well with Mr. Hand's questioning and the two are actually amiable by the end of the session. Still, the teacher relents on the question of whether or not he will flunk Spicoli, telling the stoned surfer he'll probably "squeak by."
Mike Damone and Mark Ratner speak to each other at the prom. A tenuous bond is reformed, but Damone knows he no longer has power over "Rat."
In the closing scenes, Brad is working at his new job, the bottom rung on the high school scale of after-school employment: a convenience store called Mi-T-Mart. Spicoli walks in and tries to make a purchase while fumbling with pocket change. He then asks to use the bathroom. A robber pulls up, walks in the door, sprays the security camera, pulls out a pistol and tells Brad to give him the money. Brad gets very angry as he sees this as just one more rotten episode in his disintegrating life, but he starts to open the cash register. Spicoli walks out of the bathroom and inadvertently distracts the thief just long enough for a furious Brad to throw hot coffee in the robber's face, jump over the counter, take his gun away and capture the would-be thief as the getaway car peels out the parking lot, making Brad a local hero... at least in Spicoli's eyes.
Meanwhile, Stacy, still working at the pizza joint, sees Mark at his station across the mall at the theater. She waves him over and gives him a demure photo of herself. She makes it clear she'd like to begin seeing him again. Mark is at first tentative, but Stacy playfully nudges Mark and eggs him on. He looks at Stacy for a moment, smiles and then says he'll call her.
Before the end credits roll, the characters' futures are shown:
* Brad Hamilton: Made manager of Mi-T-Mart, June 12.
* Mike Damone: Busted for scalping Ozzy Osbourne tickets. Now working at 7-Eleven.
* Mr. Vargas: Switched back to coffee.
* Linda Barrett: Attending college in Riverside. Now living with her Abnormal Psych professor.
* Rat & Stacy: Having a passionate love affair. But still haven't gone all the way.
* Mr. Hand: Convinced EVERYONE is on dope.
* Jeff Spicoli: Saved Brooke Shields from drowning. Blows reward money hiring Van Halen to play at his birthday party.