Tony Leung Chu-Wai and Andy Lau, two of Hong Kong cinema's biggest heartthrobs, play a cop working undercover in a drug triad, and a gangster pretending to be a cop. As the edgy, unshaven Leung and wannabe-yuppie Lau race against the clock to uncover one another, both take advantage of cell phones and laptops as much as guns and muscle, a device that keeps the pace quick and the action slick; even with all that technology, however, the streets, warehouses, docks, and high-rises of modern Hong Kong still ooze with industrial grit and a dark, existential malaise.