When I first saw the trailer for “Michael Clayton,” I found it to be an impenetrable mess. After seeing the movie, I understand why. It’s too complicated to squeeze into two minutes, and for that, we should be thankful. “Michael Clayton” starts with a fevered torrent of words and doesn’t let up. It’s a dark, exciting thriller, powered by a high-caliber script and a wealth of great acting and committed to telling a complex, twisted tale.

The story centers around the titular character (played by George Clooney in the latest of a string of good performances). Clayton — a “fixer” for a glitzy New York law firm — cleans up clients’ messes when they’ve done something embarrassing. He’s a worn-down man, buffeted by a sea of problems. Writer and first-time director Tony Gilroy (who wrote all the “Bourne” movies) saddles Clayton with a failed business venture, a distant family and a gambling problem. These all serve as distractions from the main, and infinitely more interesting, thread of the story: Clayton is called in to calm Arthur Edens (Tom Wilkinson), one of the firm’s best attorneys who has unfortunately gone berserk while working on a vitally important case. Edens has been representing an agribusiness, U/North, for the past six years, trying to fend off a multibillion-dollar lawsuit from the families of farmers killed by a cancer-causing weed killer. All of a sudden, he stops taking his meds, strips down naked in the middle of a deposition and starts threatening to derail the whole suit.

The performances here are universally excellent. Clooney plays Clayton with barely a smile. He manages to be haunting and magnetic, both exploiting and subverting his natural glamor. Fresh off the caress of Steven Soderbergh’s camera (in “Ocean’s Thirteen”), he seems glad to let Gilroy film him in harsh, weary light. Clooney walks through the movie wound tight, almost spitting his lines out. Clayton has hit rock bottom, disgusted by what he’s become, and Clooney wears that self-loathing well. He uses it to his advantage, making Clayton’s actions seem like the inevitable product of a life gone wrong. Clooney is challenging himself here, imbuing Clayton with ambiguity not seen in many of his previous characters while still maintaining his essential goodness.

Joining him is Tilda Swinton, mesmerizing and quaveringly villainous as U/North’s chief attorney, Karen Crowder. Swinton lets us see the terrified insecurity behind Crowder’s criminality and makes us almost root for her. Tom Wilkinson is also outstanding as Edens, tearing despairingly through the film like the heir of Peter Finch in “Network,” all wild-eyed, raving and truthful.

Gilroy has an ear for the dialogue of shadows and corruption. It’s no accident that the last movie with his name in the credits was “The Bourne Ultimatum,” which he wrote and which presented a rotted and immoral governmental apparatus doing some very Bush-like things. Gilroy’s mood and world view have not lightened in “Michael Clayton.” He situates us in a world dominated by casual cruelty, where Clayton’s boss (Sydney Pollack) can tell him offhandedly that he knew the U/North case “reeked” from the start but didn’t care.

But while Paul Greengrass shot “Bourne” up with caffeine and hurtled it around the globe at top speed, Gilroy has moved in a more traditional direction behind the camera. He doesn’t favor jagged jump cuts or split-second edits, but lets the movie unfold more slowly, anchored by its increasingly high-tension plot and dialogue. He indulges himself too much — “Michael Clayton” could have shed a storyline or two, as well as some unnecessary fiddling with the time structure — but he’s crafted a gripping drama — a welcome throwback to all the grown-up, cerebral thrillers of the 1970s like “Network” or “Three Days Of The Condor.” The final scene of the film, between Swinton and Clooney, is fantastic, a crackling back-and-forth that truly thrills with the deftness of its dialogue and the skill of its acting. Gilroy seems to be on a roll, first with the Bourne movies and now with this one. I love Bourne, but it’s a good thing we’ve also got “Michael Clayton” — where words matter more than explosions.