A paranoid, secretive surveillance expert has a crisis of conscience when he suspects that a couple he is spying on will be murdered.

Harry Caul: I'm not afraid of death, but I am afraid of murder.
[repeated line from the recording]
Mark: He'd kill us if he got the chance.
Martin Stett: [Final Line] We'll be listening to you.
Harry Caul: [upset, walking over to Martin seated] What are you doing here?
Martin Stett: Take it easy I'm just a messenger. I brought you a drink.
Harry Caul: I don't want your drink. Why are you following me?
Martin Stett: I'm not following you I'm looking for you. There's a big difference.
[last lines]
Martin Stett: [on the phone] We know that you know, Mr. Caul. For your own sake, don't get involved any further. We'll be listening to you.
[plays back recording of Harry playing saxophone]
[about a bum on a park bench]
Ann: Every time I see one of those old guys, I always think the same thing.
Mark: What do you think?
Ann: I always think that he was once somebody's baby boy. Really, I do. I think he was once somebody's baby boy, and he had a mother and a father who loved him, and now there he is, half dead on a park bench, and where are his mother or his father, all his uncles now?
Stan: What a STUPID conversation.
[first lines]
Passerby: Well, I want to go over to my place and start, you know, getting it on...
Ann: Oh, that's terrible.
Mark: Yeah. Do you ever, uh... ballet?
Ann: Be thankful. Do you have a quarter for them?
Mark: Yes, I do.
Ann: [gives it to street band]
Ann: What about me?
Mark: You'll see.
Ann: A lot of fun you are. You're supposed to tease me, give hints, make me guess, you know.
Martin Stett: I'm not following you, I'm looking for you. There's a big difference.
Ann: I can't stand it. I can't stand it any more.
Ann: This conversation is over.
Mark: Does it bother you?
Ann: What?
Mark: Walking around in circles.