“Lust, Caution” then loops back in time to 1939 Hong Kong, unfolding on a large, opulently appointed canvas that re-creates the student fervor of Hong Kong and the decadence and paranoia of pre-revolutionary Shanghai. An erotic, violent melodrama, filled with echoes of such Hitchcock movies as “Notorious” and “Suspicion,” Lee’s movie is composed of one highly flammable ingredient after another. Why, then, doesn’t it ever fully ignite? For all its hothouse passions and sometimes brutally explicit sex scenes, the storytelling seems curiously stolid, the style too movie-ish for its own good.

Lee, who won the 2006 best-director Oscar for his cowboy love story “Brokeback Mountain,” and screenwriters Wang Hui Ling and James Schamus have taken a provocative short story by Eileen Chang and stretched it into a 157-minute epic. It’s an intelligent adaptation, faithful to the themes and cruel ironies of the story, but the wrenching internal transformation at the heart of the tale—Wong’s metamorphosis from idealistic student into a conflicted femme fatale enmeshed in a torrid, sadomasochistic affair—gets overwhelmed by the overproduced melodrama that surrounds it. There’s a great, piercing story here, but too often you feel you’re watching it through the wrong end of the telescope.

The cast gives it their all. The delicately beautiful Tang, a stage and television actress from mainland China making her film debut, is convincing as both a naive schoolgirl and a woman of the world, never overplaying her hand. She more than holds her own with the veteran Hong Kong star Leung, who makes the guarded, control-freak Mr. Yee a figure of complexity and even poignancy: he flexes his power with extra vehemence knowing, deep down, he’s just a puppet to his Japanese masters. Lee, perhaps thinking of Hitchcock’s “Torn Curtain,” with its famous illustration of how hard it is to kill someone, stages an unforgettable variation on the theme: the brutal, messy, protracted murder of an informer by the inexperienced young resistance team. It’s certainly not the only striking, explosive moment in “Lust, Caution.” But you wish there were more of them.