This is Harry Caul, a loner who is a little too glum to be good company and takes his work seriously. Maybe too seriously -- which eventually proves to be his downfall. The fact that his own co-worker Stan (John Cazale) leaves him to go work for a rival agency, Moran, only serves to prove Harry is really someone who is so much a loner he drives anyone away from him. He can't seem to have any form of relationship -- it's only time when Amy will also leave him as she seems somewhat frustrated by this wall of privacy he's built around himself. His entire life revolves around secrecy, and he only is able to live vicariously throughout others, even if he himself feels guilty about it and would deny it because to top it all, he has a strong religious streak, and discloses under confession that he was witness of a surveillance gone wrong and which resulted in the deaths of three people. Now this assignment has him worried: he's listened to a conversation between a man and a woman and is afraid the woman's husband may try to kill them both.
But is this what he's heard, or has been misinterpreted due to the limitations and distortions of sound? Like 1966's BLOW UP, which dealt with what the human eye is capable of discerning through the mechanism of a camera and what happens when one zooms in, THE CONVERSATION deals with the manipulation of sound to make out a sentence that lies just underneath the sounds of the city. But while that elusive sentence comes through -- "he's kill us if he had the chance" -- what Harry fails to catch is the intonation itself, which would have radically altered his deduction and completely shifted his attention. Like the definition of the word "caul", Harry is unable to see (or hear) the reality, or that he's been a victim of his own occupation by the end of the film; by making himself visible to whom he thinks was in danger, he's now made himself the target of surveillance by the same agency who employed him as he receives that disturbing call at the end: "We'll be listening to you." Whether it be real or not, one shot implies it is: a panning shot to the right, then to the left, from an elevated angle, showing us the destruction of Harry's apartment through his own hands as he has fruitlessly tries to debug his place. It's the tell-tale pan of a surveillance camera, which he has failed to discover. Again.
This is most definitely not an action-packed thriller, but one that is totally cerebral -- it forces you to pay attention, to listen, to heighten your senses and discover for yourself what Harry is trying to find even when we know he will be wrong all along. Even as he seems to teeter over madness near the end as his grisly discovery of blood pouring out of a toilet bowl at the Jack Tarr Hotel indicates, we still wonder if he's actually seeing this, or not. Like BLOW UP, this is one of those mysteries that doesn't look to get solved cleanly, but by being inconclusive, lingers in the mind long after the credits have rolled, and in the process, leaves one man destroyed.