Failure and corruption are the glue that holds "Kill Zone 2" together, a palatably cynical movie with a saccharine silver lining. Chi-Kit Chan (Wu), an undercover cop tries and fails to bust Mr. Hung (Louis Koo), an ailing gangster with a bum ticker who tries and fails to abduct and (literally) steal the heart of his estranged brother Man-biu (Jun Kung). Chi-Kit is the film's star, but he's aided in his quest to protect Man-biu and shut Hung down by uncle Kwok-wah (Simon Yam) and Thai prison guard Chatchai (Jaa). All of these men are dirty in some way, even the heroes: Chi-Kit snorts cocaine, Kwok-wah gives bribes, and Jaa takes hush money. These crimes pave the way for the film's bleak, but never depressing outlook: people are susceptible to corruption, but they can change if they choose.

Cheang's steady hand keeps the film's exposition-heavy first half moving whenever it threatens to stall due to its top-heavy plot. There's a meandering sub-plot that connects Chi-Kit, who is imprisoned by Hung's men, and Chatchai, a crooked guard with a sick daughter. That sub-plot may seem superfluous but it's central to the film's message: everybody is connected, but not in the Pollyanna-ish way you might expect. "Sha Po Lang" takes its name from a Chinese astrological constellation that represents three elements sometimes translated as power, destruction, and lust or greed, destruction and conflict. Together, these three elements are combustive, as is evident by all the bus-related, pen-knife-centric, and candy-glass-shattering stunts that occur throughout "Kill Zone 2." Still, it's striking that what unites the principal characters isn't a will to reform, but rather a tendency towards betrayal, self-deception and violence. This isn't the martial arts equivalent of "Pay It Forward" but rather a grim beat-'em-up that combines muay thai boxing's characteristically concussive knee and elbow blows, and traditional Chinese martial arts' emphasis on graceful, dance-like choreography.

Still, you may be wondering if we need to spend so much time with Chatchai's sick daughter, especially in a film called "Kill Zone 2." You could easily ask the same question about the unusually well-developed sub-plot concerning Hung and his brother. But none of these narrative tangents really distract from the film's main narrative, since so much of the film's main thrust is discursive. In the wrong hands, "discursive" would be a polite way of saying "messy." But Cheang, a student/former collaborator of master action filmmaker Johnnie To, holds everything together admirably. His love of rhythmically-paced, wide-angle-lensed sequences shows just how much he's learned while working at To's Milkyway production company on recent hard-boiled collaborations like "Motorway" and "Accident." "Kill Zone 2" may be as cynical as early Cheang action films, like "Shamo" and "Dog Bite Dog," but it has the control and eye for detail of his superior recent work.