Married couple Rinko and Shigehiko are stuck in a sexless marriage. One day Rinko receives a letter containing pictures taken while she had been pleasuring herself. The person who sends the letter calls revealing himself as Igushi, a former psychiatric patient of hers, and begins to order Rinko to perform increasingly erotic acts. After Shigehiko finds one of Igushi's letters, he also becomes involved in the mental games--with surprising results for their marriage.