This screens as part of the Century of Chinese Cinema season and is alo being shown on 27th July.
A runaway hit in Hong Kong, this 2002 crime thriller reinvigorated the genre with its airtight script, taut editing, and sleek cinematography (Christopher Doyle served as visual consultant). Tony Leung (In the Mood for Love) plays an undercover cop who's spent three years infiltrating a local triad, and Andy Lau (Days of Being Wild) is his doppelganger, a triad mole rising through the ranks of the police department's organized crime unit. Neither man knows the other's identity, but after a while neither seems entirely sure of his own either. Their only reference point seems to be the mutual antagonism between their respective father figures, a steely police superintendent (Anthony Wong) and a scheming triad boss (Eric Tsang). In Cantonese with subtitles.
Here (and above) is the trailer.