Michael Clayton begins with its eponymous hero (played by George Clooney) summoned from a midnight card game by a colleague in Clayton’s law firm. A millionaire client has fled the scene of a hit-and-run, and the lawyer wants Michael to hasten to the client’s home and begin a mop-up operation. Though Michael has practiced law, his real forte is dealing with legal messes before they need to go to court. This is why he calls himself a “janitor,” an epithet coated with self-contempt.

As Clayton drives out of New York City to the client’s country house, cinematographer Robert Elswit makes both the city night and the country night glamorously menacing; blues and blacks have seldom been so foreboding, and James Newton Howard’s somber music keeps welling up, as if to warn our hero that the woods on either side of the road might swallow him up. But surely it’s not Michael who’s in trouble but the client, a yammering, alibi-hunting yuppie lashing out at Clayton just because the fixer can’t wave a magic wand to make trouble disappear. This kitchen conference is superbly staged and acted, with the client’s wife crumbling in the background, her face a mask of mounting shame that registers her husband’s spinelessness. Finally, just as the husband is about to whine another self-justification, the wife smashes a glass on the wall. Silence. End of argument. The shame on her face now suffuses her husband’s.

On the drive back to the city, Michael encounters a lovely sight, some horses standing almost motionless on a hillside as morning breaks. He pulls his car over and tramps up the hill for a closer look. A few blissful seconds pass. Then the car explodes. Clayton looks around wildly. Who would want him dead? Who would want to forever unfix the fixer?

Most of what follows is a flashback that answers that question. Michael Clayton is both a character study and the sort of legal thriller made popular by John Grisham and Scott Turow, and that opening sequence assures us that writer-director Tony Gilroy has the chops for either kind of movie. As the director of a thriller, he can instill anxiety in the viewer with shadows and music and sudden silences. As a delineator of character, he can turn the rich client’s wife into a Greek chorus without giving her a single line. This is a startlingly assured directorial debut. Yet, while I found this film more than promising, I also found it less than satisfying.

A maker of thrillers has to be opportunistic to the point of cynicism. Gilroy can certainly be manipulative enough: those horses materialize at precisely the right moment to save our hero. But a portrayer of psychological complexities is patient and probing, never cynical, and he wouldn’t allow those horses on the hillside to get Clayton out of his car. A maker of melodrama may be good at defining characters but the characters are nearly always in thrall to the plot. In Gilroy’s case, the best insights into the characters beg to be released from the plot.

The chief case in point is Arthur Edens, Michael’s close friend and the firm’s hot-shot senior litigator. I’ll wager that anyone reading this has had at least one Arthur Edens in his or her life (I’ve had several). Such a person is brilliant at his job but comes to question its value or morality. So he employs his professional adroitness to make war on his less scrupulous colleagues. Edens is psychologically unstable and goes berserk whenever he doesn’t take his meds; but though he may carry on like a madman, it is Arthur’s sanity that is in revolt against his law firm, for he has discovered that a colleague has “buried” a document that would lose a lawsuit for one of the firm’s clients and, worse, make the firm itself liable to be sued, even ruined. Gilroy gives Edens vivid lines but it is really the always superlative Tom Wilkinson (challenge to the reader: name an inadequate Wilkinson performance) who so adroitly poises Arthur on the borderline between vatic delusion (“I am Shiva, the god of death!”) and lucid decency. The gleam in Wilkinson’s eyes can signal either an incipient frenzy or a man liberated by the power of truth, often both at once. And that is precisely why I wanted to see a lot more of Arthur Edens than I did.

But it was inevitable that I couldn’t, for the movie is called Michael Clayton, and it’s finally a thriller about Michael’s redemption, not Arthur’s. To satisfy the melodramatic demands of the plot, Arthur’s evidence is inherited by Michael, and a sinister senior partner (Tilda Swinton, working her creepy, hooded persona to the max) sends her hired thugs after him. Hence the car explosion. But at this point something vital passes out of the movie. The mad glint in Tom Wilkinson’s eyes was more riveting than a thousand explosions.

Of course, Tony Gilroy didn’t intend his film to be solely a thriller. Michael’s decision to reveal the truth is meant to be a hard-won moral triumph over his personal interests. Trying to rescue a feckless brother from financial ruin, Clayton has secured a substantial loan from his own firm. If the firm suffers from Arthur’s revelations, Clayton might not get the money. It’s easy to see where moral choice enters in. But there is a narrative miscalculation here. At first Michael decides to suppress the evidence Arthur gave him, and he gets the loan. But when the villains mistakenly conclude that Clayton is pursuing the case, they plant a car bomb; after it fails to kill him, our hero defends himself by using the evidence. Consequently, Clayton comes across more as a man simply (and understandably) defending himself than as somebody pursuing the truth at the risk of his own neck. (Compare with John Proctor in The Crucible and Sir Thomas More in A Man for All Seasons, who pursue the truth precisely when the truth dooms them.) So it’s the villains who accidentally bring about the pursuit of truth while Michael Clayton’s inner turmoil never becomes all that interesting, despite the fact that this is one of George Clooney’s most interesting performances (his specialties-leashed anger and simmering anguish-are brought to perfection here).

None of this is meant to discourage you from seeing this movie, which possesses real verve, flashes of insight, and sheer watchability. Still, if Gilroy wants to make thrillers, he must become simpler. And if he wants to make penetrating studies of the human condition, he must allow the complexity in his writing to breathe.