Directed by Akira Kurosawa, the owner of a foundry in Japan is planning to move to Brazil to avoid a nuclear war, and his family sues to have him declared mentally incompetent.
Dentist Dr. Harada (Takashi Shimura) gets a call from the court to mediate and in the office he observes a family conflict. He learns that the wife of Kiichi Nakajima (Toshiro Mifune) wants him certified as insane because he is afraid of the atomic bombs and their radiation. He began building a bomb shelter; but then he learned that only the southern hemisphere would be safe after a nuclear war. So he began to make plans to emigrate to Brazil. The wife Toyo Nakajima (Eiko Miyoshi) and the sons Ichiro Nakajima (Yutaka Sada) and Jiro Nakajima (Minoru Chiaki), and the daughter Yoshi Nakajima are called into the office, but Yoshi’s husband and Kiichi have to wait outside.
At home Dr. Harada asks his son what he thinks about atomic weapons, and Dr. Harada says a man concerned about them is completely normal.
At the Nakajima foundry Kiichi is the boss. A farmer shows a film to the family. Kiichi goes to visit his son with a check. Kiichi says there is no chance he will be certified as mentally incompetent. He asks his son to come to Brazil with them, but he wants to stay there. Kiichi leaves and visits another mistress; but they do not want to move either. Kiichi asks his mistress Asako Kuribayashi (Akemi Negishi) to come with him. They hear the sound of thunder and become afraid.
Dr. Hayashi gets another call and is told of a second session because Kiichi is ignoring their advice and going forward with his plan. Kiichi goes home and gets letters from the court for his wife.
During the mediation they sit around a table. Kiichi is told that his plan to emigrate will not work, but he says he can trade with a family that wants to return. Dr. Harada says that moving to Brazil is not a bad idea. The sons say they were born in the plant. Kiichi says he built up the plant and would miss it the most. Kiichi says that life is the most precious thing. He says men die, but he would hate to be killed. Kiichi admits he has two mistresses and three children to support also. His son says he is terrible and tyrannical, and Kiichi starts hitting him. In the hall the family asks where their father went, and he comes back with soft drinks for them. Inside the court mediators ponder and discuss the case. Dr. Harada says a prodigal can be deemed incompetent for wasting money on women and wine, but protecting against the atomic bomb is reasonable. Psychological tests show he is sane, but others disagree and are concerned that his family may starve if he sells the foundry. Dr. Harada says it is not so simple and that they should study it. They question Kiichi, who says he is not afraid but wants to avoid being killed. Another counselor says it will be better for all to stop him. They call in the family.
In his office Dr. Harada reads about nuclear war and talks with Susumu. He says the higher court will decide. Kiichi looks at land on a mountain and considers buying it. The family uses a safe to get around their father. Kiichi asks his son for his deposit book because he needs money, but his son puts on a record. Kiichi tells his mistress that he needs 300,000, but she wants him to recognize her daughter. Kiichi asks another son for the 200,000 he sent him, and Kiichi’s mistress tries to get it for him. She hid some money and gives it to Kiichi. He says it is not enough and leaves.
The farmer tells Kiichi that he can wait. He gives him money and invites Kiichi to visit him. He says his sons opposed his moving to Brazil, but a fire made up his mind. He tells Kiichi to return the money to his sons for now. At home Kiichi gives them the money. His son says the court has frozen their assets, and what he has done is illegal. He says not to accept the money, and they fight.
Kiichi watches a plane take off and says it is easy to fly to Brazil. On a train Dr. Harada sees Kiichi and tries to talk to him. Kiichi says that he was not afraid, but after their decision he is very afraid and helpless. At his home the judge tells Dr. Harada why they had to make that decision. At the house of his mistress Kiichi holds a baby in his arms, and Mr. Kuribayashi (Kichijiro Ueda) talks about how radiation will come to Japan and about Hiroshima. He says they cannot do anything about it without money. Asako comes in and takes the baby. Kiichi sees an article about nuclear weapons and gets upset.
The family sits in a circle. Kiichi begs them to go to Brazil because H-bombs exist and war could start any time. He wants to save his family and shows a letter from Brazil. His wife says he is a good planner and that they all should go. He gets up, and his daughter gets upset and pulls him down. A doctor gives him a sedative to sleep. The Kuribayashis want to be put in his will. Others say assets cannot be transferred without his permission. While Kiichi sleeps, they discuss his will. The women look at photos of a trip to the sea, and his wife says she was afraid something bad would happen. Kiichi wakes up and hears his family discussing who might go to Brazil.
Dr. Harada learns that the foundry has been burned. Jiro blames the foremen. Kiichi in his robe says that he started the fire. They ask Sue Nakajima (Kyoko Aoyama) what happened because she was there first. She cries. Kiichi says they have enough to live in Brazil. Workers blame him, and Jiro says he is crazy. Kiichi asks them to forgive him and says he will find a way for them all to go. His daughter defends him for trying to protect them. Officers arrive, and Kiichi is put in jail for arson. Other prisoners laugh at him because of his motive.
At the Alienist Department the family walks down the stairs, and Dr. Harada apologizes for the court decision. Ichiro says they should not have taken him to court. A doctor tells Dr. Harada that lunatics are sad; but this man has made him sad. He wonders if he is the lunatic. Dr. Harada visits Kiichi in his room. Kiichi asks if there are many people left on earth. He says they must wake up and come to his planet that is safe. He looks at the sun and says the earth is burning. As Dr. Harada is leaving, Asako and her baby are arriving for a visit.
This drama reflects the subconscious fears that remain in Japan because of the atomic bombs that were exploded there and the worse hydrogen bombs that were being tested in the Pacific. A man who tries to implement a rational plan to avoid being killed by nuclear war is considered insane by most of the society that has accepted the nuclear madness as something beyond their control.