The impact of the plagiarism lawsuit against Dan Brown, author of The Da Vinci Code, could be dramatic for the world of writing and publishing.

In Britain, as in the U.S., ideas are not protected by copyright--it's the way they are expressed that counts. The accusation here is not that Mr. Brown's novel plagiarized the 1982 book's words. Plaintiff authors Michael Baigent and Richard Leigh assert that Mr. Brown wrongfully appropriated the "architecture" of their earlier work. For instance, the "Holy Blood" authors consulted documents in France relating to an alleged "Priory of Scion" organization that since 1099 has allegedly protected the secret of Jesus' marriage. Can, and did, the fruit of their labors turn up in another book?

The case is worrying to publishers and authors in part because it involves the issue of research and the point at which research becomes not just information but protected information. Depending on the judge's reasoning, a decision in favor of the plaintiffs could have a chilling effect on writers. A book (or other publication) need only appear in Britain for anyone, regardless of their nationality, to sue in a British court.

It's all the more depressing because "The Da Vinci Code" is a work of fiction, woven with legend ancient and new. So is the titillating essence of "The Holy Blood and the Holy Grail," whatever its authors say or believe. "The "Priory of Scion" documents that figure in both books' conspiracy theorizing were long ago revealed to be grounded in a hoax. One of its principal architects, Pierre Plantard, a French anti-Semite and royal-blood pretender, contributed to a partial account of the conspiracy story in a book published in 1967. So perhaps Random House should pay his heirs.