It would probably be a mistake to read too much into Ang Lee’s decision to follow up Brokeback Mountain with a film focusing so explicitly on heterosexual relationships. But this is by far the most overtly racy film in the director’s canon thus far, making all the bed-hopping in The Ice Storm look positively tame. Lust, Caution is a film about sex as communication, as struggle, as apology, even as torture. A shame, then, that there is so little genuine warmth and humanity to back it up.

The first section of the film is by far the strongest. Student Wang Jiazhi flees her rural home for Hong Kong, escaping the Japanese invasion. There she meets Kuang Yu Min, a dashing and charismatic playwright dedicated to the patriotic cause. After a soaring success on the stage, Kuang decides to use his acting troupe in the services of something more concrete – the entrapment and murder of Japanese agent Mr Yee. Wang Jiazhi agrees to act as a honey trap, luring Yee into her home so the others can finish him off.

This first act is pacy, sharp and exciting, as Wang Jiazhi grows into her role as an actress and a seducer. Tension is skilfully maintained, and the characters of Kuang and his fellow students are superbly delineated and genuinely likeable. Two key events have a shattering effect on Wang Jiazhi – firstly, an awkward and tentative bout of deeply unprofessional lovemaking with one of her fellow students, to ready herself for Mr Yee. And secondly, the startling, bloody and horrific communal murder of the traitorous Tsao, who uncovers their plan.

But after Yee’s escape and the group’s disbandment the film begins to falter. Wang Jiazhi moves to Shanghai and picks up her studies, when three years later Kuang contacts her again, asking her to resume her relationship with Mr Yee, now a key figure in the Japanese secret service. But as the two grow closer, and engage in extended bouts of explicitly depicted coupling, Wang Jiazhi begins to have doubts about her impending betrayal, culminating in a rash and drastic act which dooms her, and her fellow conspirators.

Lust, Caution was adapted from a short story by Eileen Chang, but unlike the similarly sourced Brokeback Mountain there isn’t enough plot here to sustain the film’s epic runtime. The characters, while complex, are difficult to sympathise with – we actually seem to know less about Wang Jiazhi as the film progresses, and she makes choices which seem to conflict with everything we’ve previously learned. One scene in particular, a near-rape which Wang Jiazhi seems to enjoy, is particularly perplexing, and borderline offensive. And while the more traditional sex scenes are admittedly eye-opening, one is forced to question whether it was strictly necessary to include quite so many of them.

Perhaps Lust, Caution suffers from comparison with Paul Verhoeven’s trashier, but ultimately more intelligent and entertaining Black Book last year. Or perhaps it’s a cultural divide – the film draws on an Asian tradition of erotic cinema with which Western audiences may be unfamiliar. But in the end, however beautifully shot and acted Lust, Caution undoubtedly is, the film leaves the viewer cold and unsatisfied.

Tom Huddleston