On a sweltering summer day, a gang of high school delinquents roves through Shinjuku, their restlessness cutting through the city heat. Among them, Jirō Sugita clashes with a girl, sparking a tense argument. Jirō then leaves the group and goes home to live with his single mother, Misayo Sugita. Misayo is the mistress of Keigo Nanbara, a businessman, and Jirō's growing disapproval of their relationship poisons the atmosphere at home, feeding his jealousy.
Jirō's anger erupts in a fight with Nanbara, tearing through the house and stealing money from Misayo. Toshimi Tani, another girl from the gang, has a crush on Jirō and they begin an intimate relationship, though Jirō remains mostly cool and distant toward her.
At Misayo's request, Nanbara lectures Jirō about his disreputable lifestyle, but Jirō mocks him. The following day, Nanbara, Misayo, Jirō, and his friends all head to the same Zushi beach resort, each going separately. Etsuko Shimojô, a college student desperate for money for an abortion, leads Nanbara to an empty summer home under the pretense of connecting him with Jirō to make peace. There, she strips to her undergarments and reveals her real motive: to sell herself to obtain the money she needs. The kindhearted Nanbara refuses her advances but still gives her the money she seeks. At that moment, Jirō bursts in with his mother in tow and gleefully exposes Nanbara as a philandering liar. Misayo is upset, but her love for Nanbara remains, and she begs him to stay with her. Enraged and wracked with guilt, Jirō and Toshimi flee and steal a car. Nanbara pursues them; Etsuko leaves with the money, but is waylaid by a group of delinquents who steal it from her. Nanbara finally catches up to Jirō in a hotel room, where he continues to try and reason with Jirō even as the boy alternately mocks him and kisses Toshimi in front of him. When Nanbara is undeterred, Jirō explodes and brutally assaults him with a wrench. Believing he has killed him Jirō and Toshimi escape in the car, and with the police in pursuit, Jirō begins driving at reckless speed until Toshimi screams in fear, begging to be let out of the car. He seems to have a change of heart, but then deliberately drives into the path of an oncoming truck. The moment before he dies, he screams out "Mom!"
Distraught and in pain, Etsuko collapses at the entrance to the subway and falls down a staircase. She is taken to the same hospital as Nanbara, who survived the assault, and even in his gravely wounded state begs the police to forgive Jirō for his actions. Etsuko also survives, but has a miscarriage. The next day at a local bar the youngsters frequented, a journalist for a disreputable paper tells the owner that Jirō is dead. He is disheartened with the current youth culture, but knows that the salacious details of the story will be eaten up by the public. Musing over how he will write the story, he considers starting it with:
> "Today, goodwill between people can't exist anywhere. Everything goes wrong."
