With sales of The DaVinci Code now topping seven million, it's a safe bet that Dan Brown's Catholic readership is well into seven figures. Anecdotal evidence from around the Catholic scene confirms the hunch that a lot of Catholics have read the book --- and more than a few have been disturbed by it. The question is --- why?

DaVinci's premise is preposterous: that Jesus married Mary Magdalene and appointed her the head of a movement devoted to the "sacred feminine;" thus the legendary "holy grail" was Mary Magdalene, who nurtured within herself Jesus' descendants. This "truth," ruthlessly suppressed by centuries of venal churchmen, was preserved by a super-secret "Priory of Sion," of which Leonardo DaVinci was a member. In DaVinci's famous "Last Supper," what you thought was St. John is really Mary Magdalene, the "holy grail" present at a table without a chalice.

And so forth and so on, one bizarre assertion after another --- and that's not to list the flat-footed mistakes in DaVinci, like claims that the Dead Sea Scrolls revealed new information about Jesus (the Scrolls, immensely valuable in other respects, don't mention Jesus).

Why should this ridiculous foundation for a contemporary whodunit that includes obligatory side-swipes at the conspiracy-driven Vatican disturb Catholics? I can (barely) imagine Catholics appreciating DaVinci as a kind of wild-eyed fantasy --- although the "fantasy" contains so much covert and overt anti-Catholicism that you'd have to wonder about Catholics enjoying it.

But why should reasonably well-educated Catholics find the novel's plot raising questions about their faith? What's to get disturbed about?

You remember the canary in the cage --- the old miners' trick, in which a caged canary, keeling over from asphyxiation deep beneath the earth, would signal miners that the air was getting too foul and that it was time to get out? DaVinci is a kind of literary canary-in-the-cage. The signal being sent by too many Catholics' inability to dismiss Brown's story as rubbish is that Catholics have learned to mistrust the Bible. Which is not what the Second Vatican Council had in mind, to put it gently.

The Council wanted to return the Bible to the people of the church as "their" book, an entirely worthy goal. Just when Catholics were rediscovering the Old and New Testaments, however, "historical criticism" of the Bible was breaking out of classrooms into the American cultural mainstream --- and into pulpits, where Catholic priests, newly instructed to preach on each Sunday's biblical texts, were often tempted to explain what the New Testament wasn't, rather than preaching the religious, moral and historical truths the New Testament conveyed.

The cultural and ecclesial ground was thus tilled for The DaVinci Code. If, over the past 30-some years, you've absorbed the idea that the New Testament is really elegant, inspired fiction, it's but a short step to buying Dan Brown's storyline, which is that this whole church business has been a vast, lie-driven conspiracy from the git-go. That's certainly not what mainstream historical-critical scholars intended to teach Catholics. The disturbances caused by DaVinci suggest that that's what a lot of people learned, however: they learned to be suspicious about the integrity of Christianity's basic text.

DaVinci is a problem that could become an evangelical possibility. Pastors and adult education directors might want to ensure that the parish pamphlet racks are full of an admirable brochure, The DaVinci Code: The facts behind the fiction of the bestselling novel, available from Our Sunday Visitor (www.osv.com). The brochure briskly identifies the numerous errors and historical implausibilities in the book while inviting readers to encounter the story told in the Gospels --- "the story in which the truth is, if not stranger, certainly more interesting and life-giving, than fiction." (I carry the OSV brochure in my briefcase, to hand out on planes and trains when I find someone reading DaVinci.)

Then there's The DaVinci Hoax by Carl Olson and Sandra Miesel, a new book from Ignatius Press that Cardinal Francis George of Chicago calls the "definitive debunking" of Brown's hypothesis. It's not hard to imagine an attractive adult education series being built around this able demolition job.

Dan Brown has offered pastors and teachers with nerve and wit a real opportunity. I hope they seize it.

George Weigel is a senior fellow of the Ethics and Public Policy Center in Washington, D.C.