LONDON - Like a good thriller, "The Da Vinci Code" trial has had drama, controversy and conflict. And it's ending with a cliffhanger - which way will a judge rule in the copyright infringement case against the publisher of Dan Brown's world-conquering novel?

High Court justice Peter Smith rules Friday in the claim by authors Michael Baigent and Richard Leigh against "Da Vinci Code" publisher Random House.

Smith must decide whether Brown's blockbuster "appropriated the architecture" of Baigent and Leigh's 1982 nonfiction book, "The Holy Blood and the Holy Grail." In the United States, the book is titled, "Holy Blood, Holy Grail."

Both books explore theories that Jesus married Mary Magdalene, the couple had a child and the bloodline survives. Most historians and theologians scoff at such ideas, but Brown's fast-paced mix of murder, mysticism, code-breaking and art history has won millions of fans.

"The Da Vinci Code" has sold more than 40 million copies?- including 12 million hardcovers in the United States?- since it was released in March 2003. It came out in paperback in the United States last week, and quickly sold more than 500,000 copies, an astonishing pace for a paperback release. An initial print run of 5 million has already been raised to 6 million.

A victory by Baigent and Leigh would stun the world of copyright law, challenging the concept that copyright protects the expression of an idea rather than the idea itself.

"A victory for Leigh and Baigent would make it very difficult for novelists, particularly historical novelists," said Fiona Crawley, a copyright expert with law firm Bryan Cave LLP.

"They go to source books to research the history to incorporate into their novel. It would call into question how they can research a historical novel without being accused of copyright infringement by the historian who has written the key work on that incident in history."

A win by the plaintiffs also could hold up the scheduled May 19 film release of "The Da Vinci Code" movie, starring Tom Hanks. Sony Pictures says it plans to release the film as scheduled.

If Leigh and Baigent lose, they could have to pay costs that legal experts estimate will top $1.75 million.

The case drew a packed crowd of journalists, Dan Brown fans and theological revisionists to London's neo-Gothic High Court last month.

Judge Smith retained an air of bluff good humor during sometimes esoteric hearings that touched on the Roman Emperor Constantine's deathbed conversion to Christianity, the founding of medieval warrior order the Knights Templar, the Merovingian dynasty allegedly descended from Jesus and the perfidy of a seventh-century official named Pepin the Fat.

The publicity-shy Brown traveled from New Hampshire to give evidence on behalf of his publisher, and spent three days on the stand.

Brown acknowledged that he and his researcher-wife, Blythe, read "Holy Blood" while researching "Da Vinci," but said they also used 38 other books and hundreds of documents, and that the British authors' book was not crucial to their work.

Baigent and Leigh claim Brown's novel contains the same central themes as their book. But under cross-examination, Baigent conceded that it had been an exaggeration to say that Brown used "all the same historical conjecture" as their book.

Random House lawyer John Baldwin said that while many of the incidents in "The Da Vinci Code" had been described before, "no one has put them together, and developed and expressed them, in the way Mr. Brown did. That is why he has a best seller."

Thanks to the case, so do Baigent and Leigh. Their 24-year-old book is selling 7,000 copies a week in Britain, compared to a few hundred before the case began, according to The Bookseller. Baigent's new book, "The Jesus Papers: Exposing the Greatest Cover-Up in History," has an initial print run of 150,000 copies in the United States.