Johnny is a successful banker who lives in a San Francisco townhouse with his fiancée Lisa, who has become dissatisfied with their relationship. She seduces his best friend, Mark, and the two begin a secret affair. Having overheard Lisa confessing her infidelity to her mother, Johnny attaches a tape recorder to their phone in an attempt to identify her lover by recording their phone conversations.
Johnny and Mark rescue Denny, a neighboring college student whom Johnny financially and emotionally supports, from a fight with an armed drug dealer, Chris-R. Denny confesses to Johnny that he lusts after Lisa, and though he agrees with him, Johnny encourages him to pursue one of his classmates instead.
When Lisa starts falsely claiming that Johnny has become physically abusive, Johnny becomes depressed and calls upon both Mark and his psychologist friend Peter for advice. Mark confides to Peter on the rooftop that he feels guilty about his affair. When Peter deduces that the affair is with Lisa, Mark violently confronts him on the roof's edge, only to calm down immediately.
At a surprise birthday party for Johnny, his friend Steven catches Lisa kissing Mark while the other guests are outside and confronts them about the affair. To distract Johnny, Lisa falsely announces that they are expecting a child. At the end of the evening, Lisa and Mark flaunt their affair, leading to a physical altercation between Mark and Johnny, which culminates in Johnny kicking everyone out.
Johnny locks himself in the bathroom and scolds Lisa for betraying him, prompting her to call Mark. Johnny retrieves the cassette recorder that he attached to the phone and listens to the intimate call. He has an emotional breakdown, angrily destroying his apartment and committing suicide by shooting himself in the mouth. Lisa tells Mark that they are finally free to be together, but he brushes her off for her cruel treatment of Johnny. Together with Denny, they wait with Johnny's body for the police to arrive.
