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. Meanwhile, Johnny, having overheard Lisa confess her infidelity to her mother, Claudette, attaches a tape recorder to their phone in an attempt to identify her lover.
Denny, a neighboring college student Johnny financially and emotionally supports, has a run-in with an armed drug dealer, Chris-R but Johnny and Mark overpower and detain him. Denny also lusts after Lisa, and confesses this to Johnny, who understands and encourages him to instead pursue one of his classmates. Johnny spirals into a mental haze and calls upon Peter, his and Mark’s friend and a psychologist, for help. Mark also confides in Peter that he feels guilty about his affair. When Peter asks Mark if the affair is with Lisa, Mark attacks Peter and attempts to kill him, but they quickly reconcile.
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. Johnny announces that he and Lisa are expecting a child, although Lisa later reveals she lied about it in order to cover up the truth about the affair. At the end of the evening, Lisa flaunts her affair in front of Johnny, who physically and verbally attacks Mark.
After the party, Johnny locks himself in the bathroom in despair. When he leaves, he retrieves the cassette recorder that he attached to the phone and listens to an intimate call between Lisa and Mark. Outraged, Johnny berates Lisa for betraying him, prompting her to end their relationship permanently and live with Mark. Johnny then has an emotional breakdown, angrily destroying his apartment and committing suicide by shooting himself in the mouth.
Hearing the commotion, Denny, Mark, and Lisa rush up the stairs to find his dead body. Mark blames Lisa for Johnny’s death, admonishes her for her deceitful behavior, and tells her to get out of his life. Denny tells Lisa and Mark to leave him with Johnny, and they step back to give him a moment, but ultimately they all stay and comfort each other as the police arrive.