Can Dan Brown do it again?

"The Da Vinci Code," which rattled people's notions of Jesus Christ, became a hit movie, stayed at the top of bestseller lists for years and sold more than 60 million copies, is a hard act to follow.

But Brown apparently plans to do just that with the hotly anticipated and presumably forthcoming sequel to the international phenomenon. And while readers wait for his latest mystery to unravel, they're trying solve their own: just what protagonist Robert Langdon's next quest will be.

"When I was still in the initial stages of guessing and deducing this, I concluded that it would involve the founding fathers and take place in Washington," said David A. Shugarts, author of "Secrets of the Widow's Son," one of the books already out about what readers might encounter in the "Da Vinci Code" sequel. "It was a short while after that Dan Brown himself let all that out."

More specifically, the next thriller — whose working title was initially released as "The Solomon Key," though a Random House publicist has since said that wouldn't be the name — will explore the history of the secret society known as the Freemasons and the link between it, the founding fathers and the birth of the United States, Brown has confirmed.

Several of the men who factored prominently in establishing this country were Masons, including George Washington, Benjamin Franklin, Paul Revere and others.

The clue that pointed Shugarts and others toward the Freemasons was right on the dust jacket of "The Da Vinci Code" — along with a few others Brown sprinkled on the cover to give readers some tidbits about his next book.

In the written description about "The Da Vinci Code" on the inside flap, several of the white letters are slightly bolded. When put together, they spell out "Is there no help for the widow's son?"

"The phrase comes out of the history of Freemasonry and is an emergency appeal message from one Mason to another Mason to tell each other they're in trouble — it's like 'Mayday!'," said Dan Burstein, who oversaw the publication of "Secrets of the Widow's Son" and has written other guidebooks to Brown's novels, including "Secrets of the Code" and "Secrets of Angels and Demons."

Another puzzle on the "Da Vinci Code" jacket points toward the inclusion of the founding fathers in the sequel. The anagram in dark lettering, when decoded, spells out "E pluribus unum" — an early motto for this country that means "Out of many, one."

Also on the cover are a series of geographic coordinates that turn out to be the location of the Kryptos sculpture at the CIA headquarters in Langley, Va., whose mysterious code has only partially been solved and which has long fascinated Brown and others interested in cryptology.

Symbols like the unfinished pyramid on the back of the dollar bill — taken from Egyptian history but also possibly used by the Masons — and Mona Lisa's right eye, as well as Masonic buildings like The House of the Temple in Washington and even Mormonism, could also be woven in.

And Brown has mentioned in an interview that his next novel will focus on the murders of politicians in the capital city, according to Greg Taylor, author of "The Guide to Dan Brown's 'The Solomon Key.'"

"I think it will be really interesting, especially if he sticks to what he was going to write on," Taylor said. "There's a lot on these secret societies."

Shugarts, Taylor and others theorize that part of the conspiracy that may be central to the "Da Vinci Code" sequel will revolve around the fact that as Masons, many of the founding fathers weren't Christians but rather Deists — who believe in a higher power that created life but isn't present or active in the world and doesn't interact with the human race.

That flies in the face of what many modern elected officials say about the men who established this country and its democratic government.

"The founding fathers did not mean to create a lily-white Christian nation," Shugarts said. "They had a profound respect for God but intended to allow each person to have that respect in their own way rather than make it a Christian government. Dan Brown may startle us by bringing up some of these inconvenient truths."

Some have speculated that the plagiarism lawsuits and accusations of inaccuracies in "The Da Vinci Code" have led Brown to be far more cautious in his research for his next novel.

"That whole London trial in the spring involving 'The Da Vinci Code,' in my opinion, really threw him off course substantially," Burstein said. "He doesn't want to get caught in another legal quagmire." Burstein believes it may even be possible that he's put this sequel project on hold indefinitely.

In any case, it will soon become apparent whether or not Dan Brown readers can expect the author's next offering in March 2007, the release date that has most recently been bandied about.

Burstein said marketing would have to begin by November or December at the latest considering how huge the book is anticipated to be.

Though many fans say they don't think a "Da Vinci" sequel can or will top the original, they're still excited for the next installment in the Robert Langdon series, whenever it surfaces.

"I'm very much looking forward to reading a book about American history and finding out what secret societies were out there," said Lisa Shea, who runs the "Da Vinci Code" fan Web site www.lisashea.com. "With his talent for drama, he could make it into a really cool story. I am hoping that it comes out soon because I really want to read it."