Tom Hanks stars as Robert Langdon, a Harvard symbologist in Paris for a lecture when Inspector Fache (Jean Reno) informs him of the murder of museum curator Jacques Sauniere (Jean-Pierre Marielle). This poor man has been shot and will die late at night inside the Louvre; his wounds, although mortal, fortunately leave him time enough to conceal a safe deposit key, strip himself, cover his body with symbols written in his own blood, arrange his body in a pose and within a design by Da Vinci, and write out, also in blood, an encrypted message, a scrambled numerical sequence and a footnote to Sophie Neveu (Audrey Tautou), the pretty French policewoman whom he raised after the death of her parents.

Having read the novel, we know what happens then. Sophie warns Robert he is in danger from Fache, and they elude capture in the Louvre and set off on a quest that leads them to the vault of a private bank, to the French villa of Sir Leigh Teabing (Ian McKellen), to the Temple Church in London, to an isolated Templar church in the British countryside, to a hidden crypt and then back to the Louvre again. The police, both French and British, are one step behind them all of this time, but Sophie and Robert are facile, inventive and daring. Also, perhaps, they have God on their side.

This series of chases, discoveries and escapes is intercut with another story, involving an albino named Silas (Paul Bettany), who works under the command of the Teacher, a mysterious figure at the center of a conspiracy to conceal the location of the Holy Grail, what it really is, and what that implies. The conspiracy involves members of Opus Dei, a society of Catholics. Opus Dei works within but not with the church, which also harbors a secret cell of cardinals who are in on the conspiracy. These men keep a secret that, if known, could destroy the church.

But one of the fascinations of the Catholic Church is that it is the oldest continuously surviving organization in the world, and that’s why movies like “The Da Vinci Code” are more fascinating than thrillers about religions founded, for example, by a science-fiction author in the 1950s. All of the places in “The Da Vinci Code” really exist.

Tom Hanks, Audrey Tautou and Jean Reno do a good job of not overplaying their roles, and Sir Ian McKellen overplays his in just the right way, making Sir Leigh into a fanatic whose study just happens to contain all the materials for an audio-visual presentation that briefs his visitors on the secrets of Da Vinci’s “The Last Supper” and other matters. Apparently he keeps in close touch with other initiates. On the one hand, we have a conspiracy that lasts 2,000 years and threatens the very foundations of Christianity, and on the other hand a network of rich dilettantes.

What Ron Howard brings to the material is tone and style, and an aura of mystery that is undeniable. The murder scene in the Louvre is creepy in a ritualistic way, and it’s clever the way Langdon is able to look at letters, numbers and symbols and mentally rearrange them to yield their secrets. The movie works; it’s involving, intriguing and constantly seems on the edge of startling revelations. After it’s over and we’re back on the street, we wonder why this crucial secret needed to be protected by the equivalent of a brain-twister puzzle crossed with a scavenger hunt. The trail that Robert and Sophie follow is so difficult and convoluted that it seems impossible that anyone, including them, could ever follow it. The secret needs to be protected up to a point; beyond that it is absolutely lost. Here’s another question: Considering where the trail begins, isn’t it sort of curious where it leads? Still, as T.S. Eliot wrote, “In my beginning is my end.” Maybe he was on to something.