By Dan Brown

Doubleday. 454 pp. $24.95 It is Dan Brown's considerable achievement to have written a theological thriller that is both fascinating and fun. "The Da Vinci Code" takes us in hot pursuit of nothing less than the Holy Grail, which turns out to be not the legendary Cup of Christ but a trove of documents proving dramatic facts about Jesus that the Catholic Church has been suppressing for nearly two millennia.

After Brown's hero, Robert Langdon, a Harvard professor of religious symbology, delivers a lecture in Paris, police summon him to the Louvre, where the renowned curator Jacques Sauniere has been murdered. The dead man left behind an enigmatic message that mentions Langdon's name. The scholar soon realizes that he is about to be charged with the crime and, accompanied by the dead man's predictably alluring granddaughter, Sophie, he flees.

We learn that the murdered curator was the leader of the Priory of Sion, the secret society founded in 1099 to protect the documents that the church wants destroyed lest they shake the very foundations of Christianity. Over the years, the Priory's grandmasters have included such luminaries as Sir Isaac Newton, Botticelli, Victor Hugo and Leonardo da Vinci. Da Vinci is of particular importance because he developed the highly sophisticated code that, if broken, will lead to the Grail. Given the clues left by the dead man, Langdon and Sophie set out to find the Grail, one step ahead of both the French police and a giant albino priest who killed the curator on behalf of the conservative Catholic organization Opus Dei.

The novel alternates between conventional chase scenes and the scholarly digressions that provide its special charm. Do you know, for example, why we are supposed to be fearful on Friday the 13th? Because it was on Friday, Oct. 13, 1307, that Pope Clement V sent his soldiers to capture the Knights Templar, torture them into confessing their crimes against God and burn them at the stake as heretics. Are you aware that the Catholic Church has for centuries repressed both women and the feminine side of early Christianity? During the Inquisition, for example, "Those deemed 'witches' by the Church included all female scholars, priestesses, gypsies, mystics, nature lovers, herb gatherers, and any women 'suspiciously attuned to the natural world.' . . . During three hundred years of witch hunts, the Church burned at the stake an astounding five million women."

In a great many ways, the novel has a feminist slant, as when Langdon tells Sophie: "The Priory believes that Constantine and his male successors successfully converted the world from matriarchal paganism to patriarchal Christianity by waging a campaign of propaganda that demonized the sacred feminine, obliterating the goddess from modern religion forever."

For that matter, do you know the source of the Mona Lisa's enigmatic smile, or that one of the figures in Da Vinci's "Last Supper" is a woman? Read the book and be enlightened.

Langdon and Sophie team up with Sir Leigh Teabing, a rich Englishman who has spent his life searching for the Grail. Teabing takes a very dark view of the Church's role in suppressing accounts of Christ's life: "The Vatican, in keeping with their tradition of misinformation, tried very hard to suppress the release of these scrolls. And why wouldn't they? The scrolls highlight glaring historical discrepancies and fabrications, clearly confirming that the modern Bible was compiled and edited by men who possessed a political agenda -- to promote the divinity of the man Jesus Christ and use His influence to solidify their own power base." Langdon, Sophie and Teabing race from Paris to London to continue their quest at the Temple Church -- founded by the Knights Templar in 1185 -- then at Westminster Abbey, at the tomb of Sir Isaac Newton, who seems to be at the heart of the mystery.

Brown keeps the pace fast, the puzzles that lead to the Grail are exceedingly clever, and there is a flurry of surprises and betrayals before the mystery is finally solved. Whatever the reader makes of the religious theories put forth, Brown has a great deal of interest to say about the early days of Christianity, the influence of pagan religions on it and the legend of the Grail. He says the revelations about Jesus -- not to be revealed here -- have been whispered about for centuries, but have never overcome the opposition of organized Christianity. How much of this is fact and how much is fiction? Read the book and make up your own mind. As Charlie Brown said when asked if he believed in Santa Claus, I refuse to become involved in a theological discussion.