Rikiya Shoda is an engineer working for the Atomic Agency in Japan. One day, his wife Nanako returns home with a lost teenager called Ayu. A man, pretending to be the father, comes to get her back; Ayu keeps telling him that Rikiya and Nanako are her parents. Through this disruption, Rikiya suddenly starts remembering his youth as a revolutionary.
A spontaneous romance blooms between Kawamura, a professor touring Europe, and Naoko, a married woman living in Paris, scarred by the Nagasaki atomic bombings. The two protagonists travel around Europe trying to find themselves.
Shingo and Ritsuko have a baby: Takashi. They happen to be a happy couple, but soon Ritsuko wants to know who is the true father of Takashi, born by artificial insemination.
