The Key is a novel in the form of two secret diaries, kept by a middle-aged Kyoto professor and his wife. Each knows the other may be reading, and each writes partly with that in mind. The husband, anxious about fading vigour, tries to rekindle his marriage through jealousy and daring experiments, while his wife is reserved and guarded in public but more complicated in private. A young man close to the family adds to the tension. It is a dark, ironic study of desire, privacy and deception within marriage, and it caused controversy when first published.