Der Dialog

Harry Caul (Gene Hackman) is surveillance expert in San Francisco. He is very professional and stays away from the content of what he's recording. He is extremely private and paranoid about being watched. He's a devout Catholic and a jazz lover. He has no friends other than business associate Stan (John Cazale). He's secretive even with girlfriend Amy Fredericks (Teri Garr). Director (Robert Duvall) hired him to spy on couple Ann and Mark. Martin Stett (Harrison Ford) tries to get the tapes but Caul refuses. They bring back a bunch of fellow investigators attending the surveillance convention and it's revealed that he's haunted by an incident in New York. He become concerned about what is going to happen to Ann and Mark.

This is a really fascinating character. It taps into the 70s paranoia about technology and surveillance. What starts as fascinating technical idea turns into a deeply disturbed personal struggle. It doesn't give easy answers. The audience strains to understand what's going on in the case. That's part of the appeal from Francis Ford Coppola. He lays out the cards but doesn't necessarily explain them.