Having tackled the secretive Catholic conservative group Opus Dei, Dan Brown says he's writing his next book about the Freemasons.
The Freemasons say they are simply a fraternity that aims to make good men better and to support each other. Because they are essentially secret, however, groups such as the Freemasons can stir all kinds of theories.
The all-seeing eye atop the pyramid on the $1 bill is a Masonic symbol. Some say that some of the great American buildings have Masonic symbols incorporated into their architecture.
Many of our Founding Fathers, including George Washington, Benjamin Franklin and John Hancock, were Freemasons. There are currently 1.7 million members, though membership has been declining since 1960.
Some conspiracy theorists say that the Freemasons, or Masons, have designs on government control.
"The thing people think about when they think of Masonry is secrecy. They think of this hidden order that they know almost nothing about," said Steven C. Bullock, author of "Revolutionary Brotherhood: Freemasonry and the Transformation of the American Social Order."
The Freemasons have a 500-year history. Originally, they were stonemasons who built the great cathedrals of Europe.
"They traveled widely, because a town would have a church built maybe once every hundred years," said Margaret Jacob, author of "The Origins of Freemasonry: Facts and Fictions."
"As they traveled, they had secret passwords and signs so when they came into a town and said, 'I'm a stonemason, I want to work,' they had to be able to prove they were a member of the guild."
S. Brent Morris, who is, among other things, a 33-Degree Mason, master of the royal secret and managing editor of the Scottish Rite Journal, said that although Freemasonry was not a religion, it had overarching religious principles that were part of Masons' rich traditions.
"The Freemasons did something very radical 300 years ago. We said that men can agree that God exists and he compels them to do good in their life and we can stop all religious discussion at that point and go out and do good and help mankind. So Freemasons invite any believer in God to join them."
Morris said Freemasons displayed a Bible, a Koran and a Torah on their altar. Another powerful symbol of the tradition is the sword carried by the grand sword bearer of the Supreme Council, the highest order within the Freemasons that meets every few years.
Yet the society was so closed centuries ago, is so closed still, that the penalty for revealing Freemason secrets is supposed to be gory death.
Richard E. Fletcher, the executive secretary of the Masonic Service Association of North America, said that the Freemasons was not an enigmatic organization. Things like secret handshakes date back centuries.
"The handshakes are a throwback to our early days when Freemasonry was related to actual builders and stone," he said. "That is how they prove they are a guild member, because most were illiterate."
Although there were once anti-Masonic political parties and early 19th-century President John Quincy Adams called the Freemasons a power-hungry "boa constrictor" of an organization, Fletcher said Freemasonry had always been about improving oneself. The nature of the self-reflective process is private, he said, and many people mistake that for secrecy.
"While he is being challenged to look inward at himself as a person, he is going to have to self-reflect, contemplate, think. This can't be done in a public forum," he said. "We are pledging ourselves to become better people in our home, in our churches, in all walks of life."
Throughout the centuries, the Freemasons evolved into a wide-ranging, worldwide fraternity with many members having considerable power and influence. In this country, that influence has sometimes reached all the way into the White House. Fourteen of 43 presidents have been Freemasons.
"More than one-third of the presidents belonged to the fraternity, so this is a substantial tradition of politicians being involved in Masonry, so there are fears at times in American history that Masons are too involved in politics," Bullock said.
There are all kinds of stories: that Masons wanted to control a government and thus were behind the American Revolution. Some claim that the Masons killed President Kennedy.
"These are terrific stories. They're yarns. There is not, however, a shred of historical evidence to back them up," Jacob said.
"Their grand secret is that they have no secret," Bullock said. "They're claiming that they're hiding something, but really part of the point is to pretend that you're hiding something."
Still Brown can have a field day in his next book. After all, how did a Masonic symbol -- if it is a Masonic symbol -- wind up on our $1 bill?
Some critics point to these conspiracy theories and group secrets as reasons for the drop off in Mason membership, but Morris said other organizations were experiencing a similar problem.
"It's also diminished in virtually every voluntary organization in the United States," Morris said. "When you look at all the organizations declining in membership and participation, I think you can't point to the Masonic traditions."
For more information about the Freemasons, visit their Web site.