Lethal Weapon franchise curator Richard Donner digs deep within his comfort zone to deliver a high-concept action thriller about a black guy, a white guy, and lots of gunplay. Likewise, Bruce Willis does his Brucest as the weather-beaten, half-dirty cop Jack Mosley, whose excesses have reduced him to the grunt detail of escorting a grand-jury witness to court. The witness, played with cliché-canceling charm by Mos Def, is a petty thief — but, more importantly, the case requiring his testimony is one of police corruption. Hence, Jack, who really just wants to lie down, must fend off a squad of murderous thugs commanded by his gum- and scenery-chewing ex-partner (David Morse). Even with a bum leg, Jack manages to stay a step ahead, either because he’s enlivened by the rote buddy-thriller banter or because, as his habit of chasing Advil with Southern Comfort suggests, he is a man of tactical foresight. That some of the action is too dimly lit and carelessly choreographed to follow is by no means an impediment to getting the idea — or enjoying it; the movie pays off generously and just as expected.