Ang Lee's Brokeback Mountain, with its frank scenes of gay sex, was the first major movie to open here in 2006. Two years later, his Lust, Caution, which has heterosexual scenes of almost unparalleled frankness for a mainstream picture, is the first major film to open in Britain in 2008. Like Brokeback Mountain, it will certainly end up on many lists of the year's 10 best. The Taiwanese-born Lee is a true auteur.

While moving from genre to genre, period to period (and most of his films are set in the recent or distant past), he never appears to repeat himself, yet he constantly pursues personal themes and his films contribute to a distinctive oeuvre. One of his recurrent concerns is with people facing crises, often in changing times. Another is the generational conflict between fathers and children.

The most interesting, however, is of characters forced to adopt masks, to dissemble, to conceal their true nature. This can be homosexuality (Brokeback Mountain, The Wedding Banquet), political allegiances (the superb Civil War western Ride With the Devil) or, in its most extreme form, Hulk (generally regarded as his only real failure), where the comic-book hero attempts to suppress the destructive green monster that lurks inside him.

These themes come together in different ways in Lust, Caution, which, like Brokeback Mountain, is expanded from a short story by a woman writer, in this case by Chinese author Eileen Chang, who died in California 12 years ago at the age of 74. Set in Shanghai and Hong Kong between 1937 and 1942, it's a moody espionage thriller much influenced by the Hollywood film noir, particularly Alfred Hitchcock and exotic melodramas of Oriental intrigue. But events are seen entirely from the point of view of Westernised, middle-class Chinese men and women and taking place within that community. This is not the China of Pearl Buck or JG Ballard's Empire of the Sun.

The film's central character is Wong Chia Chi (Tang Wei) who we first meet in 1942 Shanghai, posing as the sophisticated Mrs Mak Tai Tai from Hong Kong in the circle of the well-off, mahjong-playing wives of top-level Chinese collaborators living within the protected Japanese enclave. They're like the pampered wives of Nazi leaders and quislings in occupied Europe who don't inquire too closely into their husbands' activities and avert their eyes from the atrocities around them.

The horrors and humiliations of street life in Shanghai are as convincingly re-created as the cosmopolitan suavity that managed to carry on in wartime. We realise, however, that Wong doesn't quite belong to this milieu and that she has a covert relationship with Mr Yee (Hong Kong star Tony Leung), the local secret police chief, rooting out opponents of Wang Jingwei's collaborationist government…

Lust, Caution is an excellent thriller. It is also for Lee an important inquiry into the divided lives of his parents' generation. The script by Wang Hui Ling and James Schamus, Lee's American collaborator as writer and producer, is a fine piece of work. Mexican cinematographer Rodrigo Prieto, whose films include Amores Perros and Brokeback Mountain, and production designer Pan Lai have given the film a mood and appearance of cool, exotic menace. The score by French composer Alexandre Desplat, who wrote the music for The Painted Veil and The Queen, is a subtle blending of East and West with neat samplings of Hoagy Carmichael's 'Stardust' and Elgar's Enigma Variations. Lust, Caution is a triumph for international cinema.