IT’S official. A direct descendant of Jesus Christ is alive and well and living in Beverly Hills. I suspect she gets her sultry looks from Mary Magdalene’s side of the family.

She doesn’t sport a beard, and has never knowingly walked on water. But in Ron Howard’s rip-roaring film, which opened the Cannes Festival tonight, she is a top notch cryptologist with miraculous sex appeal. Good genes will out, obviously.

The thrill is that no one has the faintest inkling what on earth is going on when a glamorous cop, Audrey Tautou, and a handsomely paid symbologist, Professor Tom Hanks, are dragged to the Louvre at midnight to investigate a gruesome, ritualistic murder.

The gallery is one of many terrific locations. Gloomy oil paintings glare down from the walls at the spread-eagled body of a naked elderly man who is surrounded by blood and symbols. The dread is cleverly compounded by the fact that the mystery is elaborately hidden in the works of Leonardo da Vinci. Tautou is a dab hand at cracking arcane codes, but Hanks’ laid-back professor has the thankless task of explaining it all.

The bewildering clues trigger a frantic dash to expose the greatest cover-up before it is buried forever by crazed monks from the sinister Roman Catholic order of Opus Dei.

The investigators of the murder become prime suspects and flee for their lives. Enemies — mostly Catholics — lurk around every corner. Alfred Molina is a plump and poisonous bishop who pulls strings from Rome. Jean Reno’s evangelical FBI agent puts the fear of God into everyone he meets. But Paul Bettany’s albino monk, Silas, is an absolute peach. He chases Hanks and Tautou across Europe with a gun in one hand, and a whip to flagellate himself in private in the other. I’ve rarely seen an actor have more fun.

Thankfully, Tatou has the driving skills of Michael Schumacher. When he’s not birthing ingenious thoughts, Hanks spends most of the film looking travel sick.

According to Dan Brown, the Church has been pulling our leg for the best part of 2,000 years. His fiction rests on the “novel” idea that the Church has conspired to crush evidence of the Holy Grail along with the guardians of the secret. Unfortunately no one could mistake Brown for a serious theologian in the way that no one could mistake Ron Howard for Fellini. The story is so far-fetched it brings tears of pure joy to the eyes.

There are red-herrings galore. A multimillion pound blockbuster that starts in Paris and ends up in a hamlet in Scotland has clearly got a lot of explaining to do.

The wealth of exposition about the Priory of Sion, the Merovingian kings of France, and the Knights Templar is frankly stifling. Any thriller that can throw up the line, “I have to get to a library fast”, is in dire need of medical attention. To his eternal credit, Howard illuminates entire chapters by making them look like supper time at Hogwarts. The actors stroll through chunks of history and armies of crusader ghosts like panic-stricken students on an endless tour of Gothic churches.

Ian McKellen provides the most magnetic character. He is fabulously arch as the rich eccentric who harbours the refugees and the even greater desire to explode the greatest myth ever invented.

The good news is that if a direct bloodline to Mr and Mrs Christ were found, we could scrap Sundays and presumably lay our earthly grievances elsewhere. Yes, the film is a cat’s cradle of lunatic ideas with lashings of religious psychobabble, but it’s infinitely easier to forgive than the book that begat it.