Sounds like just another detective movie, maybe with some gratuitous breasts thrown in for whorehouse mise-en-scène. Au contraire - there is absolutely nothing gratuitous in this film. It's a thriller without the obligatory chase scene, a murder mystery without gore. Instead, Klute has actual character development, and not where you'd expect it. Our protagonist doesn't need any extra exposition: he's created entirely of ambiguous silence, plain talk that reveals some small-town naïveté, and Sutherland's brooding stare. Bree, on the other hand, is one of the richest prostitute roles in screen history, and Fonda runs with it. We listen in on her therapy sessions, see her with johns, and watch as she struggles to decide what to make of Klute. It takes a while to realize that this film, named for him, is all about her - whodunnit be damned.
The two develop a very hesitant, almost unacknowledged romance, and Klute finds himself protecting Bree from a stalker who may be his vanished friend. Cinematographer Gordon Willis (vet of The Godfather and many Woody Allen films, he's known as the "prince of darkness" because of his fondness for shooting in deep shadows) heightens this uncertaintly wherever he finds it, favoring lopsided compositions with lots of mysterious empty space in them. In his hands, even clichés - like shots from the stalker's point of view - look fresh.
Meanwhile, screenwriters Andy and Dave Lewis throw out everything that is unnecessary - including some lingering questions we have about the missing person case - and director Alan Pakula sticks to that plan, never trying to make things more clear than they should be. Klute is that rare mystery film that actually has some mystery to it after the credits roll.