The Departed.

THE DEPARTED Directed by Martin Scorsese (Warner Brothers, 2006)

Martin Scorsese doesn't believe in nations; he believes in tribes. For him all politics is local and bloody, and tribal loyalty holds together the patchwork of neighborhoods we mistake for society. In Goodfellas (Warner Brothers), manhood and membership in society are achieved by keeping a blood oath to one's gang, and in Gangs of New York (Miramax), the birth of our modern urban nation is forged in a bloody caldron of tribal wars. We are, for Scorsese, a land of "Bloods" and "Jets," an urban Balkans populated by violent men.

This time out the warring tribes are the cops and robbers, and with an extraordinary and gifted cast, Scorsese has constructed a tale of two gangs immersed in mortal combat, each with their own matching warlords, captains, and foot soldiers--and each with their own spy behind enemy lines. The hoods are led by Frank Costello (played with delicious malevolence by lack Nicholson), who has infiltrated a Boy Scout look-alike named Colin Sullivan (Matt Damon) into the ranks of Massachusetts' finest. Captain Queenan (a paternal and determined Martin Sheen) heads the trooper's tribe, recruiting an equally bright-eyed lad by the name of Billy Costigan (Leonardo DiCaprio) to run with Costello's wolves.

On the surface Scorsese's film works well as an edgy thriller, with Damon and DiCaprio playing their murderous game of cat and rat. But on a deeper level, this tribal tale examines the costs of loyalty and betrayal. Damon, who only has to pass for a hero, has the easier part, though he too knows the risks of failure and begins to pang for a life he cannot have. But DiCaprio is a man descending into hell, repeatedly forced to betray himself to pass for Nicholson's rising protege, paying an escalating and suicidal bill for his progressive alienation from himself and the tribe that has tossed him away.

If Scorsese is right, and we all live do in tribes, The Departed asks about the price we pay to belong--or leave.