There’s a wonderful poem about adultery called “Story of a Hotel Room,” by the mysterious English poet Rosemary Tonks, which ends like this:

“…someone should have warned us / That without permanent intentions / You have absolutely no protection / If the act is clean, authentic, sumptuous / The concurring deep love of the heart / Follows the naked work / profoundly moved by it.”

“Lust, Caution,” the superb new movie by Ang Lee, is of the same opinion. Based on a story by Eileen Chang and set in Shanghai during World War II, it tells the story of a plot by some Chinese students to assassinate Mr. Yee (Tony Leung), the head of the collaborationist government’s secret police, by setting a honey trap for him. But the bait, the beautiful Wong Chia Chi (Tang Wei), discovers too late that she has been caught in the poetess’s trap.

It is a scenario of almost stunning audacity. The audience is required to sympathize with a vile murderer and tyrant who routinely and without compunction tortures and executes his fellow Chinese on behalf of the country’s Japanese occupiers. Moreover, the patriotic students who want to kill the police chief come across as a bunch of pathetic amateurs and dreamers, easily manipulated by a sinister communist agent as ruthless as Mr. Yee himself.

As if all that were not enough, most of the story is told in flashback. It begins as the students are finally about to spring their long-prepared trap on Mr. Yee, then takes them up to the point where Wong gives the coded signal. Then it takes us back four years to the origins of the plot among a group of freshmen at Hong Kong University. Some two and a half hours later, we finally get back to the place where we were in the first few minutes.

Even if the characters — apart from Wong — were more sympathetic than they are, you’d think the nonlinear structure would be a sure way to lose the audience along a long and meandering way. I can’t remember the last time I sat through a nearly three-hour movie without resentful feelings that it was a good deal longer than it needed to be.

Not so with “Lust, Caution.” Everything works triumphantly. Not only does the cinematic storytelling — almost a lost art in Hollywood these days — keep you on the edge of your seat, but the atmospherics, for which latter-day Hollywood has got into the habit of sacrificing plot, character, and plausibility, knock the spots off anything the dream factory has produced in ages. This is by far the best movie I’ve seen all year.

Worth a special mention in the category of atmospherics that also advance the plot are the sex scenes. These are another example of Mr. Lee’s boldness, not only in incurring for his film the dreaded NC-17 rating, which automatically reduces its commercial potential, but also in daring the challenge of banality and triviality.

I certainly wouldn’t have thought it was possible anymore to show on-screen sex that was not merely pornographic or clichéd or both, but Mr. Lee’s two wonderful leading actors pull it off, along with their clothes and their inhibitions. Here at last is that hitherto undiscovered Holy Grail of erotic cinema, sexual imagery that really is artistically essential to the film’s serious purposes. These are to plumb the depths of the human heart and explore the nature of human sexuality, an exploration that also has political ramifications. The latter are all understated and not at all crude or propagandistic. They transcend ideology — in a way that, as it happens, Mr. Lee’s previous film, “Brokeback Mountain,” did not — by making us see its irrelevance to the real wellsprings of human action.

As a meditation on power, and what it does to those who possess it, and on sex in relation to power and trust, I don’t know anything to beat it. It’s also a movie about acting, and how the parts we play in life end up determining who we are. Oh, and by the way, it’s also a great tragic love story to rank with the best the movies have ever produced.

Finally, mention should be made of the film’s fidelity to historical truth, both moral and material (at least so far as I can tell). If the storytelling seems almost miraculous in its adherence to a dwindling standard of movie craftsmanship, the resolute refusal to impose upon the past the values and assumptions of the present seems at least equally astonishing.

All this together produces an emotional logic as compelling as the narrative logic, and it’s bound up in a perfectly neat Chinese package with a lovely original score by Alexandre Desplat that is redolent of the romantic Hollywood movies of its period, which are a recurring motif. Don’t miss it on any account.