Shortly after moving to Los Angeles with his parents, 17-year-old Jim Stark (James Dean) enrolls at Dawson High School. In the opening scene, Jim is brought into the police station for public drunkenness. When his mother, father and grandmother arrive at the police station to retrieve him, conflicts in Jim's family situation are introduced as he explains to the arresting officer. His parents are often fighting. His weak-willed father (Jim Backus) often tries to defend Jim, but Jim's picky and domineering mother always wins the arguments for his father cannot find the courage to stand up to his wife. Jim feels betrayed both by this fighting and his father's lack of moral strength, causing feelings of unrest and displacement. This shows up later in the film when he repeatedly asks his father, "What do you do when you have to be a man?"
The next day, while trying to conform with fellow students at the school, he becomes involved in a dispute with a local bully named Buzz Gunderson (Corey Allen). While Jim tries to deal with Buzz, he becomes friends with a shy 15-year-old boy, John, who is nicknamed Plato (Sal Mineo), who was also at the police station the night of the opening scene for shooting and killing puppies. Plato idolizes Jim as a father-figure much to Jim's concern. Plato tells Jim that his parents divorced several years ago and are never in Los Angeles. His mother lives away in her hometown and never visits, calls or writes, while his father (a wealthy business executive) is always traveling and avoids comming home, leaving only his housekeeper to look after Plato. Plato experiences many of the same problems as Jim, such as searching for meaning in life and dealing with his absent and selfish parents who "don't understand."
In the school hallway, Jim meets Judy (Natalie Wood), whom he also recognizes from the police station the previous night, where she was brought in for being out alone after dark, who originally acts unimpressed by Jim, saying in a sarcastic tone, "I bet you're a real yo-yo." She is apparently the property of Buzz. Judy too has an unhappy homelife when it shows her before going to school when she deals with her unattenative and sexist father who gives all his attention to Judy's younger brother as well as ignors both Judy and his wife for he feels that women are ment only to serve him, and nothing more.
That afternoon, Jim goes on a field trip with his science class to the Griffith Observatory. At the Planetarium, he watches a dramatic presentation of the violent death of the universe. After the show, he watches Buzz and his thugs slash a tire of his car for no reason, and then Buzz challenges him to a knife fight, while the gang taunts Jim as a "chicken." Jim reluctantly takes part in the fight and wins, subduing Buzz by holding his switchblade up to his neck before discarding both knifes off a railing. Both Jim and Buzz get slight injuries during the knife fight. Not to be outdone, Buzz and his thugs challenge Jim to a "Chickie Run" with Buzz and Jim racing stolen cars towards an abyss. The one who first jumps out of the car loses and is deemed a "chicken" (coward).
That evening, the "game" is held with Judy and several students in attendance to watch. But the race ends in tragedy for Buzz when a strap on the sleeve of his leather jacket becomes looped over a handle on the car door, preventing him from jumping out before the car goes over the cliff.
Jim runs home and tries to tell his parents what happened, but quickly becomes frustrated by their failure to understand him and storms out of the house. Jim goes to the police to find the sergeant who took his statement the previous night to tell him about the accident involving Buzz's death, but learns that the police officer is not there. Jim refuses to speak to any policeman and will speak only to the sergeant and he leaves. But Jim is spotted leaving the station by three of Buzz's friends, Crunch (Frank Mazzola), Goon (Dennis Hopper), and another one of Buzz's gang members whom is not named. Mistakenly thinking that Jim told the police about the "Chickie Run", they decide to hunt Jim down to "silence him"... permenently.
Jim meets up with Judy and they go to an abandoned mansion to hide out. Plato finds them there (he was the one who told Jim about the house). There they act out a "fantasy family," with Jim as father, Judy as mother and Plato as child. However, Crunch, Goon, and the other boy soon discover them, and terrorize Plato who finally brandishes his mother's handgun that he took from the house, shooting Crunch, and at Jim, and a police officer who investigates, in a clearly unstable state.
Plato runs and hides in the Observatory, which is soon besieged by the police. Jim and Judy follow him inside, and Jim convinces Plato to lend him the gun, from which he silently removes the ammunition magazine. When Plato steps out of the observatory, he becomes agitated again at the sight of the police and charges forward, brandishing his weapon. He is fatally shot by a police officer as Jim yells to the police, too late, that he had already removed the bullets. Plato was wearing Jim's jacket at the time, and as a result, Jim's parents (brought to the scene by police) think at first that Jim was shot. Mr. Stark then runs to comfort Jim, who is distraught by Plato's death. Mr. Stark promises to be a stronger father, one that his son can depend on. Thus reconciled, Jim introduces Judy to his parents and they drive off together as dawn starts to break.