The great editor and film theorist Walter Murch once divided the ensemble picture into two categories. The first is the “divergent” narrative, where a core cast of several characters are intertwined in the film’s beginning and then diverge as the story progresses (think “The Godfather” or “The Royal Tenenbaums”). The second is the “convergent” narrative, where a core cast of several characters begin without knowing each other and end up intertwined, either literally or symbolically (“Nashville,” “Magnolia”).

Clint Eastwood’s latest film, “Mystic River,” audaciously manages to dodge both of these categories. It begins in the 1950s, as its three leads (each one a protagonist of sorts) play street hockey as kids. A very, very disturbing and traumatic incident follows — to give it away would be to rob the reader of the intensity of this moment when viewing the film.

Flash forward to the present day: the three boys — Jimmy, Sean and Dave — are grown-ups with wives. The ensemble expands. Yet the men do not diverge. A murder prevents them from separation.

“Mystic River” is works in the tradition of the great Shakespearean tragedies. There are quite a few characters to keep track of, yet somehow the movie feels like it boasts a smaller, more intimate cast. This is because the acting in the film is probably some of the best of 2003.

Tim Robbins and Kevin Bacon deliver fine performances, while Sean Penn is solid in every scene, bellowing and crying after his daughter is murdered. Marcia Gay Harden (winner of the Best Supporting Actress Oscar in 2001 for “Pollock”) and the perpetually underrated Laura Linney shine despite their lesser roles. And finally, Laurence Fishburne takes a break from his “Matrix” persona to take on a more challenging role as a detective.

As its title suggests, “Mystic River” places much importance on setting. I would go so far as to say that the city of Boston is another character in the film’s varied ensemble. The sense of patriotism, the working class setting, and the richly textured Boston accents crafted by Penn and Robbins all help distinguish the setting of the film from other cities that could house the intense story.

Eastwood often uses the setting as a character in his films. His overlooked “Midnight in the Garden of Good and Evil” (1997) skillfully utilized the city of Savannah, Ga. That film is also a murder mystery, but it bears few other similarities to “Mystic River.”

Over the past three decades, Clint Eastwood has established himself as one of the most versatile actor-turned-directors to emerge from Hollywood. His films range from reworking the American Western (1992 Oscar-winner “Unforgiven”) to tender love stories (1995’s “The Bridges of Madison County”).

Of course Eastwood’s acting talents have been heralded for years. As a filmmaker, though, he is a master of allowing maturity and elegance to grace less generically mature genres. (His 1976 western “The Outlaw Josey Wales” is among the only politically correct American westerns.) And Eastwood’s role as music composer on “Mystic River” proves his versatility knows no bounds.

For all its greatness, “Mystic River” has several flaws. The film fails to provide a lighter balance of comic relief with its seemingly constant, heavy drama. Many viewers also might be distracted by several loopholes in the plot. And yet, if so many millions of viewers could digest “The Usual Suspects,” which is the king of loophole-plagued film mysteries, it is unlikely that “Mystic River” will be a problem.

“Mystic River” is one of Clint Eastwood’s finer efforts. Its intense drama is delicately handled. It has the tonality of a classical film noir and the punch of an episode of “Law & Order.” The film is a great murder mystery. It assumes its audience is patient enough to let it take them where it wants to go.

A note for cinephiles: Make sure to watch for an 88-year-old Eli Wallach in an uncredited bit role as a liquor store owner. This marks the first collaboration between Eastwood and Wallach since they starred opposite each other in the 1966 masterpiece ‘The Good, the Bad, and the Ugly.” A-