Sinsuke, a man living in an apartment complex, accidentally witnesses his neighbor, married woman Saya, committing adultery. Her actions shock and unsettle him, as she had always given the impression of being serious and pure. Internally, Sinsuke mutters, "She seemed so proper and innocent, yet she's bringing men into her home... You can't judge a book by its cover." Seizing the opportunity, he begins plotting to control Saya completely. He thoroughly investigates the identity, occupation, and daily routines of her lover, then threatens to harass the man if Saya disobeys him, gradually forcing her into submission. Though his methods are underhanded, to Sinsuke, they are a necessary means of asserting control in an unfair situation.