I must confess to being somewhat disappointed in this, since it's been touted as among the best "conspiracy thriller" films. It has its moments, but the specifics of the paranoid elements all get rushed out at the end, and there are some gaping plot-holes. For example, Joe Turner (Redford) is able to meander into a telephone exchange without a problem, and for no apparent reason, also possesses the technical skills to wire 50 phones together in series, to prevent the CIA from tracing him. Not bad for a guy whose job is to read thriller novels - at least, up until his entire office is wiped out, while he's out getting sandwiches. He's then forced on the run, taking Kathy Hale (Dunaway) hostage and holing up in her apartment while he tries to work out who he can trust, and what to do.
It's only when they reveal the reason why they're after the hero - and, boy, has it acquired some nice resonance, thirty years later - that you've something into which you can get your teeth. Otherwise, it's all too vague, with the Turner-Hale relationship almost laughably shallow: one minute he's tying her up, the next they leap into bed together. Well, I guess he's Robert Redford - in 1975, that came with baggage attached (like, say, Tom Cruise now). Von Sydow is, however, excellent as the hitman on Turner's tail, whose interest in his target is directly tied to who's paying. In many ways, it's the Night of the Living Dead of conspiracy thrillers; almost the first of its kind, soon after Watergate, and deserves respect for that. But like Night, it's also a genre that's developed since, and the script for this seems somewhat clunkly and ill thought-out in comparison to modern examples.