For his directorial debut, veteran screenwriter Tony Gilroy (2007's "The Bourne Ultimatum") has compiled a heavy-hitting crackerjack ensemble headed by George Clooney (2005's "Syriana"), Tom Wilkinson (2006's "The Last Kiss"), Tilda Swinton (2007's "Stephanie Daley") and Sydney Pollack (2002's "Changing Lanes"). A dream cast, for sure, and one working at the top of its game in "Michael Clayton," a complex and demanding legal drama that will go over the head of anyone not paying close attention. The type of film where the viewer spends more time mentally putting the whats, hows and whys of the plot together than actually sitting back and actively enjoying what he or she is seeing, writer-director Gilroy ultimately rewards the patient with a spot-on denouement as smart as it is satisfying.

Michael Clayton (George Clooney) has been working for seventeen loyal years with Kenner, Bach & Ledeen, one of the top law firms in all of Manhattan, but his name won't be showing up on any court cases anytime soon. A "fixer" specializing in cleaning up other people's mistakes and dirty work, Michael's latest task is his most daunting yet: to put a cork on the improper behavior and damaging findings of guilt-stricken attorney Arthur Edens (Tom Wilkinson). Initially acting as defense in a class-action lawsuit against crooked agrochemical corporation U/North, Arthur's conscience finally gets the best of him after stumbling onto information proving that U/North is to blame in the ailments and deaths of hundreds. As Arthur's psychoses fractures, Michael struggles to work out the needs of U/North litigator Karen Crowder (Tilda Swinton) and supportive law firm co-founder Marty Bach (Sydney Pollack). Worn-out and cynical from dealing in a dirty, if highly compensatory, profession and trying with little luck to be an available father to young son Henry (Austin Williams), Michael has no idea how dangerous things are about to get.

It is more typical for a film to start off well and fall apart in the end rather than the other way around. "Michael Clayton," however, features a humdinger of an opening and closing and a somewhat dry middle act. Following a first-scene narration delivered by Arthur Edens about the epiphany he experiences over his cold-blooded, dishonest profession—this alone is more chilling than most horror movies—a prologue gets underway that slyly misleads before turning back the clock by four days and readjusting its core premise. The movie then starts to drag its feet the deeper it digs into the ins and outs of all the legal (and illegal) wrangling. Writer-director Tony Gilroy earns credit for trusting the brain power of his audience instead of spelling everything out, though there are times when a little up-front clarity in regards to the details of the lawsuit and the stances of a few of the characters wouldn't have hurt. Once the narrative edges toward meeting up with where it began, "Michael Clayton" becomes riveting stuff all the way until the gratifyingly acidic ending.

George Clooney is brilliant as Michael Clayton, quite an endorsement since he sometimes tends to play versions of himself (see 2001's "Ocean's Eleven," 2004's "Ocean's Twelve," and 2007's "Ocean's Thirteen"). Here he is full-blown chameleon, his outwardly confident body language and internally shifty discomfort a compelling mixture. Michael Clayton is the best at what he does, but there's no nobility in his job description and the constant demands take him away from being the kind of dad he knows he should be. Clooney's scenes with Austin Williams (2006's "The Good Shepherd"), excellent as the impressionable Henry, are piercingly effective, particularly a car chat where Michael pleads for him to make an honorable future for himself, his decidedly grown-up words uncertainly being processed by a little boy who doesn't yet know how important what his dad is trying to say is.

As Arthur Edens, Tom Wilkinson ravenously chews through his role without tipping his hat to his character's true level of sanity. Tilda Swinton is electric as Karen Crowder, a mess of insecurities and doubts behind closed doors who has sold her soul to the devil. Her final confrontation with Clooney is as good as it gets in the acting and writing departments. Finally, Merritt Wever (2002's "Signs") leaves a lingering and sympathetic impression with only two scenes as Anna, a Midwestern farm girl and potential witness in the lawsuit who gets caught in a difficult situation when she decides to fly to New York on Arthur's dime.

With the exception of the questionably-intended symbolism of horses in a key sequence, the various lofty plot threads that make up "Michael Clayton" are well-established and nicely integrated into a whole. The more one thinks about the film, the more its positives shine through. That's a good thing, as the script wavers on the technical side, the pacing is too deliberate in parts, and the morally corrupt characters aren't the easiest to warm up to. Still, director Tony Gilroy has made an efficient and, in a way, unexpected first motion picture. For a movie that initially wears its emotional frigidity like a badge of honor, "Michael Clayton" blindsides you at the end when, lo and behold, you discover that you've actual grown to care about and be invested in the title character's life. All that is left to do is hope for the best.