I've read a few comments here that seem to imply that N x NW is lacking in depth or missing some kind of transcendent meaning. It's only "entertainment." That seems unfair. If you want introspection or soul-searching, rent an Ingmar Bergman for heaven's sake! Hitch was always the master of surfaces, the perfect artifice. When an actor once asked "What is my motivation in this scene?" Hitch replied, "your salary." He had no use for heavy-handed meanings and morals, even in his dark fables.
Still, N x NW is full of them if you look. The shallow ad-man discovers he's actually an intrepid hero. Truth be told, he's as world-wise as he is world-weary. Can you imagine forgiving and even pursuing a lover who has lied to you so she can send you off to be killed? Who seduced you "just following orders?" How romantic is that? He eventually realizes he's caught in a terrible game of moral relativity, with everyone out for themselves or their cause, so he might as well join them. It's in the forest reunion, after the fake shooting, where he pronounces judgment on it all: "If you fellows can't lick the Vandamms of this world without asking girls like her to bed down with them and fly away with them and probably never come back alive, maybe you better start learning to lose a few cold wars!" So Thornhill is a mensch after all. Who knew?
That's why the earlier scene in Washington at the CIA building is so important, and, contrary to some opinions, needs to be there. That's where you first realize how ruthless the whole Cold War game is. "We do .nothing," the Professor pronounces, about Thornhill's predicament. "C'est la guerre," one of them intones ironically. "Goodbye, Mr. Thornhill, wherever you are," says the last. It doesn't ruin the movie for us to discover that Kaplan doesn't exist. We had about 40 minutes of uncertainty. Now it's onto some other intrigue. Hitch gives us plenty. It was a favorite Hitchcock ploy to let the viewer in on a secret that the protagonist didn't know. From that point on, the viewer is subconsciously willing that inside information to him or her, and wondering when and how they will discover it.
There are so many ironies in N x NW it's hard to list them all. Maybe the greatest is Vandamm. He seems like the epitome of cool and control and sophistication. Yet he's constantly miscalculating! First he nabs the wrong guy, then he fails to kill him on at least three occasions, in part because of a kinky predilection for exotic homicide like crop-dusting biplanes and drunken convertible driving, (and knife-throwers, if you believe as I do that Vandamm's thug Valerian was actually aiming for "Kaplan" and missed). How this guy got to the top of his game is a true mystery.
But Vandamm's biggest screw-up is loaning out his girlfriend for the night on the train. She's obviously long over him and eager to move on, whether she knows it or not. And Vandamm's even met the intriguing, resourceful hunk he's turning her over to! And he's not worried? Talk about arrogance and vanity! So he loses Eve as well. Still, once Leonard informs on her, he could save his own butt if he just "disposed" of her in some normal Mafioso kind of way—like a bullet or something—but instead he has to fantasize about throwing her out of the plane over the ocean. That gives our hero the extra five minutes he needs to save her. One more irony.
So think of Vandamm's dénouement: there he is, this suave foreign agent whose gig is undermining our government, busted atop the very icon of Americana, Mt. Rushmore, all his thugs dead, his mistress in love with someone else, and now probably about to be put away for life (and maybe even executed in those paranoid 1950's times), when just a few moments before he was happily sipping champagne in his ultra-modern Frank Lloyd Wright mountain retreat. Talk about reversal of fortune!
At least he still has the panache to quip a final one-liner, as his "right arm" Leonard hurtles over a cliff. "That wasn't very sporting, using real bullets."
Ernest Lehman's brilliant script and convoluted plot makes this movie one I can watch again and again. The acting is superb and nuanced, all the way down to the minor characters. And I haven't even mentioned Bernard Herrmann's masterful score. Another post!