In Los Angeles during the mid-1950s, teenager Jim Stark is arrested and taken to the juvenile division of a police station for public intoxication. At the station he crosses paths with John "Plato" Crawford, who was brought in for killing a litter of puppies, and Judy, who was brought in for curfew violation. The three separately reveal their innermost frustrations to the officers; all three of them suffer from problems at home. Jim feels anguished by his constantly bickering parents, Frank and Carol, but even more so by his timid father's failure to stand up to Carol; the issues are further complicated by Frank's interfering mother. His frustrations are made manifest to officer Ray Fremick when Jim is released to their custody.
Judy is convinced that her father ignores her because she is no longer a little girl, so she dresses up in racy clothes to get attention, which only causes her father to call her a "dirty tramp", while Plato's father abandoned his family when he was a toddler, and his mother is often away from home, leaving Plato in the care of his housekeeper.
On the way to his first day at Dawson High, Jim again meets Judy and offers her a ride. Seemingly unimpressed by Jim, she declines and is instead picked up by her "friends", a gang of delinquents led by Buzz Gunderson. Jim is shunned by the rest of the student body but is befriended by Plato, who comes to idolize Jim as a father figure.[7][8]
After a field trip to Griffith Observatory, Buzz provokes and challenges Jim to a knife fight; Jim bests Buzz by knocking his switchblade out of his hand, then throws his own blade away. To preserve his status as gang leader, Buzz suggests stealing some cars to have a "Chickie Run" at a seaside cliff.[9] At home, Jim ambiguously asks his father about defending one's honor in a dangerous situation, but Frank advises him against confrontation of any kind. That night, during the chickie run, Buzz plunges to his death when the strap on his jacket sleeve becomes entangled with his door-latch lever, preventing him from exiting the car. As police approach, the gang flees, leaving Judy behind, but Jim persuades her to leave with him and Plato.
Jim confronts his father while his mother watches.Jim later confides to his parents his involvement in the crash and considers turning himself in. When Carol declares they are moving again, Jim pleads with Frank to stand up for him. When Frank refuses, Jim attacks him in frustration, then storms off to the police station to confess, only to be turned away by the desk sergeant. Jim drives back home, finding Judy waiting for him. She apologizes for her prior treatment of him due to peer pressure, and the two begin to fall in love. Agreeing to never return to their respective homes, Jim suggests they visit an old deserted mansion Plato told him about.
Meanwhile, Plato is intercepted by three members of Buzz's gang, who are convinced that Jim betrayed them to the police. They steal Plato's address book and pursue Jim; Plato retrieves his mother's gun and leaves to warn Jim and Judy, finding them at the mansion. The three new friends act out a fantasy as a family. Plato then falls asleep, and Jim and Judy leave to explore the mansion, where they share their first kiss. Buzz's gang find and wake up Plato, who, frightened and distraught, shoots and wounds one of the gang. When Jim returns, he attempts to restrain Plato, who flees, accusing Jim of abandoning him.
Plato runs to the observatory and barricades himself inside as more police converge including Fremick who, with Frank and Carol, have been searching for Jim. Jim and Judy follow Plato into the observatory, where Jim persuades Plato to trade the gun for his red jacket; Jim quietly removes the ammunition before returning it, and then convinces Plato to come outside. When the police notice that Plato still has the gun, they shoot Plato dead as he charges them, unaware that Jim had removed the bullets. Frank comforts his grieving son, vowing to be a better father. Now reconciled with his parents, Jim introduces them to Judy.
