If you've had your head in the world lately, you'll know that Dan Brown's book "The Da Vinci Code" is, pretends to be or is accused of being a lot of things. But while it may be heretical (and certainly is a work of fiction), for all its calculated puzzles and conniving villains, it's no literary marvel, simply a tight, fast-paced thriller. This is the one thing Academy Award-winning director Ron Howard's ("A Beautiful Mind") new film version is not. So dark the con of man indeed.

Howard's adaptation is a classic underachievement. Here we have beach reading dressed up as a literary epic, lightening-quick narratives bogged down by winding explanations and needlessly elaborate flashbacks, and a fantastically lurid plot mechanically and unconvincingly blunted. But while it does fail on many levels, Howard's film is ultimately successful in doing the one thing any summer blockbuster worth its weight in ticket stubs had better do: entertain. Not a moment elapses without tension and every scene goes by engulfed in suspense.

A modern-day scavenger hunt of considerable historical consequence, "The Da Vinci Code" centers on the approximately real-time adventures of Robert Langdon (two-time Academy Award-winner Tom Hanks) and Sophie Neveu (Audrey Tautou, "Amelie"). Langdon is a Harvard "symbologist" who is in Paris to give a lecture on, well, symbols, when he is abruptly intercepted by the French police in connection with a murder at the Louvre. Seemingly trapped in the consequence of a crime he had nothing to do with, Langdon is assisted by Neveu, a cryptologist with the French police who harbors seemingly endless secrets.

As Langdon and Neveau race through the night, solving puzzles the dead man intended them to find, the bizarre murder grows evermore mysterious. Aided by an old Englishman named Sir Leigh Teabing (Sir Ian McKellen, "The Lord of the Rings"), the pair uncover an impossible plot, of which "the greatest coverup in human history" is only the beginning.

The film succeeds in creating an air of indiscernible mystery and then of grand revelation, but it does so far more tediously than necessary. The biggest problem seems not to be Howard's often-confused direction or even Hanks's unexpectedly bland performance, but the utter incoherence of Akiva Goldsman's screenplay. Goldsman - who won an Oscar for "A Beautiful Mind" and also collaborated with Howard on last year's critically acclaimed "Cinderella Man" - appears mortally bound to Brown's words, never taking the initiative to make the film come alive, nor providing the actors the space to do so on their own.

Never is this more true than for Langdon. Hanks's many great performances have always been the result of him defining the character he played and not allowing himself to be forced into a role already molded. Given that Langdon was a living, breathing character well before the film ever began production, perhaps Hanks wasn't the best choice in the first place, but there's no denying that Goldsman's uninspired, constricting writing failed him.

The other characters, played by a superb cast, seem similarly tied down. Tautou is likable, but fails to shine or command. Her relationship with Hanks is all-too artificial, forced to absorb lines like "I've got to get to a library, fast!" As Bishop Aringarosa and Captain Fache, respectively, Alfred Molina and Jean Reno are both strong, but still nothing more than storyboard cutouts, rattling off Goldsman's consistently banal and often inconsequential dialogue.

But McKellen and Paul Bettany ("Firewall") are somehow spared. McKellen uses his special combination of British snobbery and wisdom to create a character at once funny yet introspective, heroic yet cowardly. Perhaps it should be no surprise that he rose above mediocre writing so easily, having been the force that kept Peter Jackson's often-lagging narrative in "The Lord of the Rings" witty and believable. Bettany - who plays Silas, a murderous monk and needless to say, the most bizarre character in the film - gives his role a hint of supreme tragedy, making Silas a victim of the schemes of bigger men, rather than simply a homicidal lunatic.

Dan Brown's novel is a social phenomenon that has brought up questions about the fine line between righteous questioning and heresy and factually based fiction and fact. Howard's film, though it is an entertaining, middle-of-the-road blockbuster, is pressured to shy away from that controversy and often does so by recklessly hacking at the source material rather than carefully trimming around it. It's far from a failure but a disappointment all around, bogged down by the urge of everyone involved not to alienate anyone. This is the fate of mainstream films that raise even hints of controversy: the unfortunate clash of creativity and reality.

The Da Vinci Code
At the Showcase and Quality 16
Columbia

Rating: 2 and 1/2 out of 5 stars