Set in 1956, a middle-aged professor Soichiro and his young wife, Ikuko, suffer from an unfulfilling sexual relationship. The man believes he can unlock the secrets to her passion and says so in his diary. Although he puts his diary away, he leaves the key where his young wife can find it. One of his ideas is to invite a young photographer named Kimura over hoping that his presence will spark his wife's interest. That night, a nervous Ikuko faints after drinking too much. Soichiro escorts her to the bedroom, where, seeing his wife's naked body for the first time, makes love to her. When she cries out Kimura's name, Anzai feels at once tormented and incredibly aroused. He writes all of this down and, eventually, his wife reads his thoughts. This inspires her to create a diary of her own which he, in turn, reads. A pattern develops in their newly eroticized marriage whereby Kimura comes over, the three talk and drink until Ikuko faints; Soichiro makes love to her.