By Kathy McCormack
The Associated Press

The Da Vinci Code, a thriller by a relatively unknown author, is a best seller. It has boosted the profile of author Dan Brown - and it's brought his first literary challenge.

Lewis Perdue says Brown's story, which explores codes hidden in Leonardo Da Vinci's artwork and a closely guarded secret involving the Roman Catholic Church, has similarities to Perdue's Daughter of God, published in 2000.

Last week, Perdue sent a letter to Doubleday, Brown's publisher. While religious themes, secrets and conspiracies aren't newcomers to popular fiction, Perdue said he was seeing too many of his own ideas in The Da Vinci Code, Brown's fourth novel.

"There are far too many parallels between the two books for it to be an accident," Perdue said. "We've decided to take legal action."

Brown said that until last week, he had never heard of Perdue, who has written about a dozen books, including The Da Vinci Legacy, which deals with a church secret involving the illegitimate offspring of St. Peter.

Brown's protagonist, who made his debut in a previous novel, is a professor who studies religious symbols. Perdue's hero is a professor of religion. Brown's heroine is a cryptologist; Perdue's is an expert specializing in art forgery. Both deal with curator deaths.

"To me, the biggest smoking gun is there is a painting which contains, physically, a gold key, which leads to a safe deposit box in a Zurich bank, which contains the ultimate clue leading to the treasure," said Perdue. "And the two people retrieve this from the safe deposit box as the bad guys are closing in and they escape by the skin of their teeth."

"Swiss bank accounts are so often in thrillers they are cliche," said Brown, who added that there are limited places to hide a key in an art museum.

Brown said his first book about his professor, Angels and Demons, came out before Daughter of God. Perdue said Daughter of God is a re-edit of his 1985 book, The Linz Testament, with the same hero but with a different name.