I got it--it's NOT about the plot!

Exactly. Remember when audiences automatically realized that movies were about both the plot AND the characters? It wasn't difficult to figure out; you just followed the film and understood both.

The movie is about a woman living as a prostitute in New York, and the dilemmas she faces: continue making quick money as a call girl or become an actress/model or marry the nice businessman from Pennsylvania or succumb to heroin addiction like the rest of her hooker friends. In order to make the story more interesting and sell more movie tickets, the producers placed this drama within the larger context of a suspense thriller: Where is Grunemann? Why did he disappear after seeing Bree? Is he stalking her, or is it someone else? And if it is someone else, who is he, and why is he stalking Bree, and does he have anything to do with Grunemann's disappearance...and is Bree in grave danger??? It is a great formula for both critical and commercial success.

There is a scene in which Klute calls Bree's psychiatrist's office and is told she left a forwarding number. He then tries to get it from the reluctant secretary. This is about the same time as the killer is playing the tape for Bree. I assumed that Klute eventually got the phone number, found out who it belonged to (at this point he would get the building and floor location) and went there. Granted, it all happens too fast, I don't think he would have enough time to do all that and still show up in the nick of time to save Bree unless the building is literally next door.

Austin Powers? what?

I agree 100% with rmanlius- I just watched this on my DVR last night and even though I really liked it, the things you mentioned totally took me out of the film. All the workers just let Bree stay in the office while they left? They didn't lock up? The elevator can be used at any time by anyone? Wow, I guess the business was just lucky NYC is such a safe city and burglary and theft aren't a problem. And the scene where the answering service gave Klute the phone # Bree was at? Yeah, that would really happen. And why wouldn't the operator go ahead and tell him she said she was only going to wait for 5 minutes before leaving? She would have already been long gone! The climax falls apart, complete with a tacked on happy ending.

Maddy,

Yes, that is it. She did not believe in her own redemption because all around her led her to think no one else was achieving any redemption. She even questioned her therapist's ability to achieve anything (although of course WE see it was her fault she was not improving until the latter part of the film).

Also on the point about character development, themes related to that, and the plot, it does seem to me there are few films today that successfully combine that. My favorite films of the last ten or twelve years include Lost in Translation, which many complain has no real plot (I disagree, but that's not the point), and No Country for Old Men, which many complain does not clearly ally its plot with its themes (such disagreement being indirectly made in the way there is so much disagreement about the connection between the narrative and the thematic). I disagree with the criticisms of those films, but my main point is there are so few films which even try to combine those elements.

Klute is not the greatest film of the seventies. But it does succeed at making that combination.