Harry Caul (Gene Hackman), a detached and paranoid surveillance expert who finds himself becoming a victim of the same modern technology he uses to destroy others. It begins with a seemingly routine job trailing an unfaithful wife and her lover. But when Harry visits the husband’s office to deliver the incriminating tapes he’s made of the couple, his client’s assistant tries to intercept him. Harry refuses to hand over the recordings and suddenly discovers that he may have captured a conversation about something that’s a lot more important than adulterous goings on.