As unit sales for established bestsellers like Stephen King, Tom Clancy and Michael Crichton have eroded, publishers and booksellers have been feverishly scanning the midlist for the next breakout thriller. Though every season brings new contenders, it's unusual for a novel by a relatively unknown author to spark intense discussion among a wide cross-section of booksellers, months ahead of publication. But that's what has happened with Dan Brown's fourth novel, The Da Vinci Code (Doubleday), set for publication on March 18, while many bigger names are still hanging back from the February 2 laydown of John Grisham's King of Torts.

Unfolding like a tightly constructed puzzle, the plot begins with the murder of the Louvre's chief curator, and hinges on clues hidden in plain view in the works of Leonardo da Vinci. As Harvard symbol expert Robert Langdon and the curator's granddaughter, Sophie Neveu, are drawn more deeply into the case, they find themselves on a quest across Europe not just for the truth behind one of Christianity's most dramatic cover-ups, but for the Holy Grail itself. What keeps this baroque conceit from collapsing is the way Brown grounds it in historical facts about da Vinci's life, along with two actual secret societies: the Priory of Sion, a pagan brotherhood to which da Vinci belonged, and a contemporary, Vatican-sanctioned Christian sect called Opus Dei.

"I was drawn in based on the genre, and became fascinated by the subject matter," said Jill Miner, co-owner of Saturn Booksellers in Gaylord, Mich., who admitted to sitting down on the job because she couldn't wait until she got home to finish the book. "I was never sure how much was fiction and how much fact. There's no better compliment I could pay to a book like this."

Three booksellers at The Muses in Morgantown, N.C., were so excited that The Da Vinci Code returned to the art historical and religious themes of Brown's second novel, Angels and Demons, that they all read the same ARC at once. The store had handsold numerous copies of the earlier book, though its overall sales amounted to only about 12,000 copies in hardcover when Pocket published it in 2000. At one point, owner Kelly Treiber even had to fend off a customer buying three copies of Angels and Demons for his friends. Upon learning that The Da Vinci Code featured the same protagonist, the man offered $30, then $40 and finally $50 for the ARC before she convinced him it was not for sale and took his preorder for the $24.95 hardcover.

At the Borders Group, suspense buyer Dan Mayer saw the book's power to generate excitement firsthand. "I first heard about it last August from a Ballantine rep who had read 100 pages, and then from a Bantam rep, even though neither one was selling the book to me. It's been a long time since so many people have been buzzing about a book," he said. Inside the chain, the novel quickly caught on. "Our CEO loved it, and so did his wife. Our general legal counsel said it was best book I'd ever given him, and his son really got into it, too," said Borders publicity director Ann Binkley. Added Mayer, "I think The Da Vinci Code is going to take the prize this winter. It definitely fires on all cylinders."

For Barnes & Noble fiction buyer Sessalee Hensley, front-of-store placement was a safe bet not just because of the wide support the book won at the chain's regional managers meetings, but because she's "never had a book about the Knights Templar or the Holy Grail that didn't work. It's one of those hidden subjects with enduring appeal that makes for an easy buy in both fiction and history," she explained.

After giving out 5,000 ARCs at the regional shows and in the field last fall, Doubleday received an outpouring of positive responses to the book from more than 300 booksellers, and returned to press for 4,500 more to fill demand, according to v-p and sales director Madeleine McIntosh. But it wasn't just the ARC that won over booksellers: Brown also appeared at dinners with strategic retailers around the country, and personally called many others who supported the book.

For the house, the response is especially sweet because The Da Vinci Code is not burdened by the need to earn back an excessive advance. Senior editor Jason Kaufman, who had published Brown's previous two books at Pocket, quietly brought the book with him when he joined the Doubleday staff in 2001. "He didn't know what he had until Dan delivered the first hundred pages," recalled McIntosh, who read the partial manuscript last summer at Kaufman's request, and quickly distributed copies to all the reps in her sales group, even those who don't sell Doubleday. "I called it our book of the year, and made it clear that I was staking my reputation on it," said McIntosh, who plans to print 215,000 copies.

For Doubleday's reps, the book's lay-down date will be Da Vinci Code day, meaning they will devote themselves entirely to making sure that booksellers are opening their boxes and displaying the book. "We haven't done this before for a breakout book," explained McIntosh, "though we've done it for John Grisham and Danielle Steel." The house will round out its campaign with print ads in the New York Times, USA Today and in five major markets, along with a Web-based "Crack the Code" contest and six-city author tour.

Despite Doubleday's considerable show of force, this publishing story still has a cliffhanger: will the extraordinary bookseller buzz behind Da Vinci allow it to outperform another thriller that's tapped to break out this season, James Siegel's Derailed (Warner, Feb. 19)? Though that book doesn't have the same kind of grassroots support, it's received enthusiastic early reviews, and is backed by a $500,000 TV ad campaign designed by the author, who's also an advertising executive. Only time and the bestseller lists will tell which comes out on top.