Klute

...a study of alienation: the coldness of the detective, the disappointment of the hooker and the fanatical dementia of the killer.

The movie is about a skilled, intelligent, cynical, and personally troubled New York call girl who does not, for once, have a heart of gold.

When a research scientist turns up missing, his best friend, John Klute (...), a small-town police detective, goes to New York City in search of Bree Daniels (...), a prostitute to whom the missing man had written letters.