Dennis Lehane's best-selling 2001 novel ''Mystic River'' wanted very, very much to be a Shakespearean tragedy set on the mean streets of South Boston, and it ultimately succeeded almost in spite of those ambitions. In adapting the book into the grim powerhouse of a movie that opens today, director Clint Eastwood has retained both its weaknesses and its strengths. This is at bottom a pulp thriller that strains -- sometimes pretentiously, at other times with gutter magnificence -- to reach the level of basic human truths. Like the title river, it's murky and unrelenting, and what it brings to light is not pleasant to confront.
Most impressively, Eastwood and screenwriter Brian Helgeland (''L.A. Confidential'') have retained the dark heart of Lehane's book: the way that damage can cascade down the generations, losing reason but acquiring malignant force as it goes. ''I know in my soul I contributed to your death, but I don't know how,'' mourns Jimmy Markum (Sean Penn), the tightly wound ex-con addressing the teenage daughter he has lost to senseless murder. The awful part is that he's right.
The defining event in ''Mystic River'' takes place further back, in a brief prologue set during the three protagonists' childhood. Jimmy, Sean Devine, and Dave Boyle (played respectively by Jason Kelly, Connor Paolo, and Cameron Bowen) are hacking around on the block one day when Dave is taken away by two men who appear to be plainclothes cops. They're not. The Dave who comes home is not the same person who went off in that car, and Eastwood uses the boy's half-finished signature in a slab of sidewalk cement as a visual remnant of an interrupted life.
Sean (Kevin Bacon) has grown up to be a police detective with a busted marriage; he doesn't have much to do with the old neighborhood anymore. Jimmy has run a corner grocery since getting out of prison, and if he has disbanded the criminal gang he used to command, he's still something of a local kingpin, with a ferociously devoted wife, Annabeth (Laura Linney), and three daughters. The oldest, Katie (Emmy Rossum), is from an earlier marriage, and she's planning to elope with her kindhearted boyfriend, Brendan (Thomas Guiry), when her battered body is found in the park. This happens to be the same night that Dave (Tim Robbins) comes home to his wife, Celeste (Marcia Gay Harden), covered in blood.
That's a lot of setup, and ''Mystic River'' sometimes squeezes its exposition out like toothpaste from a tube. The murder itself is not shown -- Rossum is graceful, then gone -- but Eastwood is more interested in the old wounds the murder reopens. Sean is assigned the case with his partner (Laurence Fishburne, going heavy on the donuts) and finds himself butting heads with Jimmy, who has launched his own unofficial investigation with the help of local pitbulls the Savage brothers. Eventually both men find themselves circling their old friend Dave.
The forces that Katie's murder sets in motion are unstoppable, and the film and its actors are at their best when acknowledging the tragedy of inarticulate men banging their heads against fate. Penn, an ersatz frosting of gray on his temples, is the centerpiece, and he delivers a mesmerizing, if initially mannered, performance as a noble man reclaimed by evil. Among the ghosts the movie conjures up are the Marlon Brando and Elia Kazan of ''On the Waterfront.'' In a sense, Eastwood and his cast have refashioned that pillar of blue-collar agonistes for a generation without hope.
The local specifics, it should be noted, are both dutifully trotted out and beside the point. Once you get past references to the Sox and the Cantab -- and the shock of seeing Brendan, a Herald reader if ever I saw one, buying the Globe -- the film could be taking place within any urban lunar landscape. The infamous accent varies from actor to actor, but there's nothing to match the horror that was Rob Morrow in ''Quiz Show.'' For the record: Linney nails it, Robbins comes close, and Penn's all over the map.
Bacon doesn't even bother to try. It doesn't matter: He's so good and so unshowy that you forget you're watching Bacon (with Penn you marvel at both the actor and the performance). Robbins, for his part, has his meatiest role in years as a tormented boy walking around in a grown man's skin. The film's final half is a grueling, occasionally forced journey toward inevitable spasms of violence -- and Eastwood hasn't helped himself with the tinny musical score he has composed -- but if you're going to make an essay on men brooding, these are the actors to play it.
It's somewhat odd, then, that you come out of ''Mystic River'' stunned by its female roles: by Linney as a strong man's stronger wife and Harden as a woman eventually moved by fear and secret lust to commit an unforgivable act. It's here that both Lehane and Eastwood make their play for classic tragic irony, and it's here -- in a simple, devastating look that passes between the two women during a neighborhood parade -- that ''Mystic River'' finally succeeds.