Time Out says
When first published in 1956, the sexual explicitness of Junichiro Tanizaki's novel Kagi (The Key) provoked a scandal; it was, however, most resourcefully adapted by Ichikawa, his screenwriter spouse Wada and their collaborator Hasebe. Out went the revealing husband and wife diaries that shaped a psycho-sexual power struggle; in came a serious comedy of desire, as elderly antiquarian Nakamura engineers his wife Kyo's infidelity with their daughter's medic fiancé Nakadai in the hope that jealousy will revive his flagging virility. The film cannily shifts through different points of view, as separate personal agendas (the wife's controlling lubriciousness, the doctor's scheming ambition) emerge in a bitterly witty quadrille, where the older partners are decidedly more daring than the younger generation. Actually, the film's wry observation allows for little sense of the grotesque, opting instead for the ultimate irony - one mixed with compassion and sly admiration - that such rejuvenating vivacity may not be altogether good for one's health.