Toru Nakanishi is in his third year at a university. He lies to his ex-girlfriend Mami Higashiyama that he is trying to get a job at a top advertising agency.

Broken-hearted and depressed Kyoko meets the kind and handsome young man Kadono, who she subsequently marries. Their marriage is a happy one, until Kyoko begins to suspect that Kadono may be in love with someone else.

本片根据日本官能作家谷崎润一郎的同名原作改编。《键》讲述大学教授年事渐高，体力和精力渐渐匮乏。与之相对，他的老婆郁子则正值青春盛年。教授回首过望，感叹妻子的保守和夫妻生活的单调，他将真实想法写入日记，并有意让郁子看到，希望以此唤醒妻子蓬勃的欲望。某日，女儿敏子的朋友木村来访，教授刻意让木村和郁子独处，让嫉妒激发了自己渐渐消失的欲望和能力。这片刻重焕青春的错觉令教授更加沉迷其中，他的危险游戏不断升级，妻子在这一过程中逐渐从被动转为主动。为了虚幻的极乐，教授全然不顾身家性命……