A deceptively simple idea lies at the heart of this complex thriller: the Hong Kong police and a triad gang both have an informer in each other's organisation: whoever's man picks the enemies' spy first wins the game for his side. Add to that the customary double-agent-doesn't-know-which-side-he-is-on-anymore subplot (doubled, of course), and you have plenty of ingredients for a plot, although it's to the movie's credit that although a little stylised, it never seems false or contrived. Fast-paced and bold, with a generous score, it never insults the viewer's intelligence either, and features just the right level of moral ambiguity. At one level, it's just another thriller, and there's little in the way of wider political or social subtext; but on the other hand, it's a textbook lesson in the art of making this sort of film.