With Mystic River, Clint Eastwood continues one of the most fascinating of all American directorial careers and certainly the most significant of contemporary times. Because that career has met with so much commercial success, he has been able to extend it far beyond the age boundaries of most American filmmakers, quite a break for film lovers since beginning with Unforgiven he entered into his richest period.

     Mystic River is based on a novel by Dennis Lehane, but structurally and thematically it falls right into a familiar pattern. Eastwood’s gift is that he can return to this pattern again and again without repeating himself. Each treatment is a significant variation and extension, his more structured filmmaking approach bearing a strong similarity to jazz improvisation.

     Eastwood’s tone does shift, often radically, from film to film, a practice that appears to make some people uncomfortable, though it certainly doesn’t affect the quality of his films. His just completed trilogy on aging ranged from introspection (1998’s True Crime) to comedy-adventure (2000’s Space Cowboys), to what was essentially a morose romance disguised as a mystery (2002’s Blood Work).

     Mystic River harkens back to 1993’s guilt-driven drama, A Perfect World. Set in a tough Irish neighborhood on the Mystic River which, in the movie, is identified as Boston, a geographic impossibility, and which is no doubt Somerville, we’re introduced to three kids playing street hockey: Jimmy, Sean, and Dave. Taking a break to write their names in some wet cement, they’re interrupted by a rough-speaking adult who says he’s a cop but is, to us if not to the kids, obviously up to no good. He and a partner take Davey away, ostensibly to his parents, but in actuality to a hidden basement where they molest him for four days before he escapes.

     From there, the movie flashes forward 25 years to the present day. Jimmy is a small-time gangster, disguising his illegal activities behind the façade of a neighborhood spa (small market). Sean (Kevin Bacon), has left the old neighborhood completely behind, and has become a detective with the Massachusetts State Police, partnered with Whitey Powers (Laurence Fishburne). Davey (Tim Robbins), meanwhile, has turned into a bit of a lost soul, a doting father who teaches his kid the intricacies of baseball and takes him to Fenway when he can scrape the money together, but who is always in a bit of a daze, can’t keep a steady job and is a source of unceasing anxiety to his wife Celeste (Marcia Gay Harden).

     Although it’s been years since Jimmy and Sean have seen each other, they’re still caught in a nexus of guilt over the day they suspected something evil was up, but did nothing to help save their friend Davey from it. But Jimmy, who is supposed to be the lord of the neighborhood, plunges even deeper into wells of guilt and shame when his daughter, on the day of her sister’s wedding, is found murdered in the local park. This crime brings Sean back into the neighborhood when he’s assigned as chief investigator and, nearly simultaneously, Davey becomes more of a factor in Jimmy’s life when Celeste insists on become consoler-in-chief to Jimmy and his ambitious wife Annabeth (Laura Linney).

     It’s tempting to describe Eastwood’s direction of the film’s initial principle sequences – Davey’s kidnapping and the events leading up to Jimmy’s daughter’s murder and the discovery of her body – as tours de force. But that phrase implies mere virtuosity, the empty display of skill, when Eastwood’s technical mastery is always in thrall to a larger purpose.

     Essentially, Eastwood uses loose framing, long takes, different focal lengths, and quietly elegant camera movements to establish a unified a group of characters. He then brings in another character, or group of characters, in opposition to the first, and uses editing to separate a character from one group and insert him into the other. Of course, it’s not as bloodless as all that. It’s downright chilling in the Mystic River’s opening scene, when Davey is abducted by the pedophiles.

     But it can also become enormously complicated. When the three old friends meet up again as adults, it’s not a simple, friendly reunion. Sean and Jimmy are extremely wary of one another, given their positions on opposite sides of the law, and Davey is so far removed from the sharper realities of life that he seems beyond reach. Moreover, they have become parts of other groups now. Sean, who is separated from his wife, associates mainly with Whitey and, through him, the police. Jimmy has a larger network of family and criminal associates. Davey has his son and, less so, his wife.

     As these groupings become more complex, so do the social relationships, the personalities, and therefore – and therefore is an important word – Eastwood’s style. The filmmaker has always favored triangular compositions, using split diopter lenses to negotiate difficult situations where he needs to keep multiple characters in simultaneous focus, especially in low light. This becomes increasingly necessary as the crimes of pedophilia and murder lead to more crime as Mystic River’s action progresses.

     As it does progress, Eastwood’s major theme comes into play. Essentially building on ideas he worked on with his mentor, Don Siegel, the filmmaker has always examined the extent to which someone who wishes to avenge himself (or, significantly, herself; see Sudden Impact) on an evil, must assume the tactics of that evil. And then, once having done so, what price does the avenger pay? Where does the act of vengeance leave him/her morally and emotionally?

     From early days, Eastwood has preferred, when possible, to play this issue out with three characters: The two principle antagonists and a witness. One aspect of his genius has been his ability to shift the function of his characters among those three types, which is exactly what he does in Mystic River. Throughout the movie, Sean, Jimmy and Davey take turns acting out the different roles; even Celeste steps in and takes a turn at a crucial moment. This explains the three-way compositions and diopters. They aren’t a stylistic flourish, but an extension of Eastwood’s world view, literally his artistic vision.

     Mystic River is not just a magnificent film, but another magnificent film in what would be an unbroken line of them if it weren’t for Midnight in the Garden of Good and Evil (oh, well). What gives it an extra dose of power is the harness of guilt that weighs upon its characters and the stubborn wildness with which they resist it or sorrowful acceptance with which they bear it. Appropriately for a river, its currents are powerful but steady and broad.