“The Da Vinci Code” is a direct descendant of ancient mystery cults and the arguments that would proclaim Christianity a mystery cult. For those who have not read the book by Dan Brown, the plot centers on a trio of conspiracies. One is led by a group guarding an ancient secret that threatens to undermine Christianity. Another by those who want to destroy the evidence. Yet another by those who want to expose the secret. All three conspiracies are intertwined and unlikely alliances emerge. The entangling and unwinding of these alliances is gripping and surprising – the stuff of a solid thriller.

Tom Hanks plays Robert Langdon, a brilliant art historian. I understand that many regard Mr. Hanks as one of the finest actors of our time, but here he is horribly miscast. In “Saving Private Ryan,” Mr. Hanks played a warrior so hardened that the soldiers he commanded could not believe he had been a schoolteacher before the war. But Mr. Hanks played his character so that it was hard to believe he could be anything but a schoolteacher. In “The Da Vinci Code,” his character again seems a simple schoolteacher – rather than an expert art historian.

Langdon becomes embroiled in the contest between the three conspiracies when he is summoned by the police to Paris’s Louvre Museum in the middle of the night.The curator has been murdered, and it soon develops that Langdon is himself a suspect. In order to escape capture and prove his innocence, Langdon sets off to follow a trail of clues left by the murdered curator. He is joined by the curator’s granddaughter, played by the delightful Audrey Tautou. They’re out to find the real killer, but more importantly: they’re on a modern day quest for the Holy Grail.

Ms. Tautou projects intelligence and delicacy. During her scenes with Mr. Hanks, we see a genuine friendship developing. When she places her hands on Mr. Hanks’s head to comfort him, there is no doubt that his affliction will be relieved. Her physical beauty and the grace in the smallest of movements gives this scene an intimate feeling.

Their quest moves through Paris to the French countryside, into London and then back to France. I’m not sure if a movie has ever failed so fully to take advantage of its locations. The bright spots are when the characters enter shadowy churches; The architecture is so compelling that even the filmmakers’ worst instincts couldn’t dull these scenes down to the rest of the cinematography.

The untangling of the clues left behind by the curator and his co-conspirators is a bit too neat. Each step along the way pushes all too clearly toward the next step, and each code or puzzle is too easily resolved by the cryptographically brilliant Langdon. But the pursuit of the pair – by those who seek to interfere or overtake their quest – provides genuine thrills. Much of them are provided by the sudden appearances of the dark-robed, murderous albino monk who is cleverly used by more than one of the conspirators.

As with so many stories centered around conspiracies, a distracting plausibility problem haunts “The Da Vinci Code.” If the leaders of a covert council within the Catholic church believe there is a secret that undermines their faith and the authority of their church, why do they remain so piously committed to the church? Is it power? As someone once pointed out, the Pope doesn’t have any battalions. Money? Investment banks have shown us that there are far easier ways of making and preserving enormous wealth than carrying on a 20-century fraud. Influence? It would be easier to own a movie studio or a television network. In short, the role of the conspiracy within the Catholic church in the film makes little sense. But neither do the other conspiracies.

Perhaps the strangest and least plausible of the conspiracies is the one that seeks to protect the secret from destruction at the hands of the rogue Catholic cabal or exposure by the anti-Christians. Why keep preserving the evidence of a secret that is never to be revealed? Here we are back in the realm of the mystery cult, where the secrets of the faith are known only to the initiated.

This is, ultimately, the appeal of “The Da Vinci Code”- the promise that those who follow its hero and heroine along will be admitted to the sacred order and learn the secret doctrine. It’s what drew the ancient Athenians to worship at altars to unknown gods. Hopefully enough of the film’s audience has been well-educated in the faith that Paul brought to Athens, so as not to mistake it for the mystery cult of this thriller.