This is part of the Alan Pakula Paranoia Trilogy at the Prince Charles and is screening from a 35mm print. Full details here.
As close to a classic as anything New Hollywood produced, Alan Pakula's 1971 film tells of a small-town detective who comes to New York in search of a friend's killer. The trail leads to a tough-minded hooker who can't understand the cop's determination. Donald Sutherland works small and subtly, balancing Jane Fonda's flashy virtuoso technique.
Here (and above) is the trailer.