Kenji Kenmochi (Nakamura) is an elderly professor of antiquities, now semi-retired. Advancing age has robbed him of his libido and his ability to sexually satisfy his much younger and extremely good-looking wife Ikuko (Kyo). Kenji is going to young Dr. Kimora (Nakadai) and receiving injections, which are failing to restore his sex drive but which are pushing his blood pressure to dangerously high levels.
While treating Kenji, Kimora has been courting the Kenmochi's young daughter, Toshiko. One evening when he is visiting the Kenmochi home, Ikuko drinks way too much alcohol. She excuses herself from dinner, goes to the bathroom, and runs a bath, only to pass out while naked in the bathtub, fortunately with her head above water. As Kenji and Kimora pull Ikuko out of the bath, Kenji notes the doctor's reaction to his attractive nude wife, and more importantly, his own reaction to Kimora's reaction—the idea turns him on. Kenji hits on an idea: push his wife into an attraction with the handsome doctor, then use his own arousal at the prospect to revitalize his own sex drive.
Extremely unfortunate consequences ensue.
Based on a Japanese novel called The Key. In 1983 the source novel was made into an Italian film titled The Key.
- As You Know: Kenji's other doctor makes sure to tell Ikuko that her husband is "the foremost authority on classical art objects", just so the audience knows what Kenji does for a living.
- Beware the Nice Ones: Hara, the meek, elderly servant to the Kenmochi family, knows exactly what is going on and exactly what Ikuko is up to. After Kenji dies, she poisons Ikuko, Toshiko, and Kimora.
- Breaking the Fourth Wall: The film opens with smarmy, arrogant Kimora looking straight at the camera, giving the audience a lecture about how the human body breaks down with age. He then states directly that "this is a story" about a man who couldn't accept the inevitability of getting old. Then the story starts as Kimora turns away from the camera and starts treating Kenji, his patient.
- Bratty Teenage Daughter: Toshiko, although her age is a little vague (the actress was actually 23). She is generally surly and rude around her parents, and she's obviously jealous of her gorgeous mother—with cause, as events ultimately prove.
- Can't Hold His Liquor: Ikuko is a lightweight who will pass out after moderate drinking. Once Kenji goes full perv he starts encouraging his wife's alcohol consumption so he can take advantage of her while she's unconscious.
- Chekhov's Boomerang: The insecticide and cleanser cans. One's in a red can and the other's in a green can, and it is established that Hara is color-blind and can't tell the difference between cans. Hara decides to switch the contents of the cans so that she doesn't mix them up. What happens? Well, Tomiko decides to kill her mother and her faithless fiancé, so she doses their tea with poison—except that the poison is actually the cleanser, so all she does is give their tea a funny taste. However, it turns out that in addition to illogically switching out what's in the cans, Hara also quite logically marked the poison can with "poison" on the bottom. After looking at the bottom of the can and confirming that it is in fact poison, Hara dumps it on top of the salad, and thus murders all of the other three.
- Dude, She's Like in a Coma: At the very least, Kenji is taking pictures of his wife in the nude while she's passed out. It's strongly implied that he actually rapes her while she's passed out.
- Erotic Film:
- About as erotic as a Japanese film could get in 1959 (which was notably more erotic than a Hollywood film), dealing with jealousy, sexual frustration, and the often unclothed body of Machiko Kyo.
- Kimora reveals to Toshiko that her father had Kimora develop nude photos of her mother. Not only does Toshiko insist that he show the photos to her, she is clearly turned on by them, and continues to stare at them while they have sex.
- Establishing Character Moment: Early in the film Ikuko sees a kitten poking its head through the door. She goes to set out milk for the little kitten, until it comes inside and reveals that it is hobbling with a broken front leg. Disgusted, Ikuko chucks the kitten out. Notably, her husband Kenji walks with an obvious limp.
- Gold Digger: Dr. Kimora isn't really attracted to Toshiko, and while he does have the hots for her mom, his real motivation is to have Kenji's family set him up in private practice. When he finds out after Kenji's death that the Kenmochi household was flat broke, he's desperately wondering how to get out of the situation.
- Inner Monologue: A moment right before Kimora dies, in which his inner monologue is wondering why he was poisoned too.
- Kubrick Stare: Toshiko shoots one at Ikuko and Kimora when she thinks, incorrectly, that she has poisoned them with the tea.
- The Loins Sleep Tonight: Kenji, who looks to be at least a quarter-century older than his thirty-ish and very attractive wife, can't get it up anymore. He takes rather extreme and ill-advised measures to change that.
- Out with a Bang: Toshiko knows exactly what is going on, accusing Ikuko of using her own sexuality and the weird little triangle that she has with Kenji and Kimora in order to provoke Kenji into a fatal stroke. Not long thereafter Ikuko quite deliberately and successfully does exactly this, getting Kenji to have a stroke during sex. When this doesn't quite work, as Kenji is bedridden but still alive following the stroke, she strips naked by his bedside one night and succeeds in provoking another, fatal stroke. She gives a smirk of triumph after realizing that Kenji is in fact dead.
- Police Are Useless: The cops simply cannot process the idea that an elderly grandma housekeeper could murder three people, even after Hara confesses in full, saying that she put the insecticide in the salad. So they let her go.
- Rape Discretion Shot: A naked, semi-conscious Ikuko reaches her hand up to Kenji's neck and calls him "Kimora." He grins evilly and says "It's working." The film cuts away as he's getting on top of her.
- Scenery Censor: On two different occasions in which Kenji is staring at his nude, prone, unconscious wife, his body is carefully blocked so as to obscure Machiko Kyo's naughty bits.
- Toplessness from the Back: How Ikuko is shot when she strips naked in order to trigger Kenji's fatal stroke.
- Visual Innuendo:
- After Kimora climbs on top of Toshiko (while she is still staring at nude pictures of her mom!) the film cuts to shots of trains in the nearby train station. Specifically, multiple shots of train cars—coupling. Followed by a shot of a steam whistle going off.
- The key to the back door that Ikuko gives Kimora, along with an explicit invitation to visit her for sex after everyone else has gone to bed, is a somewhat more subtle visual metaphor.