The lodge room of the Naval Masonic Hall is a colorful and somewhat inscrutable sight for the nonmember, with its blue walls, Egyptian symbols, checkered floor in the center and high ceiling painted with gold stars.

Countless secrets supposedly have been shared in this and thousands of similar rooms of the Masons around the world. Facts of life have been debated, honors bestowed, rituals enacted. You would need to belong to a lodge to learn what really goes on.

Or you could simply ask.

“The emphasis on secrecy is something that disturbs people,” says Joseph Crociata, a burly, deep-voiced man who is a trial attorney by profession but otherwise a Junior Grand Warden at the Grand Lodge of Free and Accepted Masons of the District of Columbia.

“But it’s not a problem getting Masons to talk about Masonry. Sometimes, it’s a problem getting them to stop.”

Despite all the books and Web sites dedicated to Freemasons, the Masonic Order has been defined by mystery, alluring enough to claim Mozart and George Washington as members, dark enough to be feared by the Vatican, Islamic officials, Nazis and Communists. In the United States, candidates in the 19th-century ran for office on anti-Mason platforms and John Quincy Adams declared that “Masonry ought forever to be abolished.”

And now arrives Dan Brown.

Six years after Brown intrigued millions of readers, and infuriated scholars and religious officials, with “The Da Vinci Code,” he has set his new novel, “The Lost Symbol,” in Washington and probed the fraternal order that well suits his passion for secrets, signs and puzzles.

Brown’s book, released Tuesday, has an announced first printing of 5 million copies and topped the best-seller lists of Amazon.com and Barnes & Noble online. At Kramerbooks in Washington, about two dozen copies were purchased the morning it went on sale and the store expects to easily sell out its order of 150 books.

In “The Lost Symbol,” symbolist Robert Langdon is on a mission to find a Masonic pyramid containing a code that unlocks an ancient secret to “unfathomable power.” It’s a story of hidden history in the nation’s capital, with Masons the greatest puzzle of all.

Brown’s research for “The Da Vinci Code” was highly criticized by some Catholics for suggesting that Jesus and Mary Magdalene conceived a child and for portraying Opus Dei — the conservative religious order — as a murderous, power-hungry sect.

The Mason response could well be milder. Brown goes out of his way in “The Lost Symbol” to present the lodge as essentially benign and misunderstood. Masons are praised for their religious tolerance and their elaborate rituals are seen as no more unusual than those of formal religions. The plot centers in part on an “unfair” anti-Masonic video that “conspiracy theorists would feed on … like sharks,” Langdon says.

“I have enormous respect for the Masons,” Brown told The Associated Press during a recent interview. “In the most fundamental terms, with different cultures killing each other over whose version of God is correct, here is a worldwide organization that essentially says, `We don’t care what you call God, or what you think about God, only that you believe in a god and let’s all stand together as brothers and look in the same direction.’

“I think there will be an enormous number of people who will be interested in the Masons after this book (comes out),” Brown said.

Crociata and other Washington Masons expressed amusement, concern, resignation and excitement about Brown’s novel. Crociata anticipates a “page-turner,” like “The Da Vinci Code,” and assumes, for the sake of a “good read,” that Brown will make the Masons seem more interesting than they actually are.

Fellow Mason Kirk McNulty can’t wait to read the novel: “Dan Brown is a writer of fiction; he’s not writing an article for the Encyclopedia Britannica. Whatever he says is OK. But it would be better if he says something nice about Freemasonry.”

Mason Michael Seay says some members are “not pleased about all the hoopla,” but sees the attention as a chance to “get our story across.” Lodge member Darryl Carter says he expects some “artistic license” and senses from conversations with other Masons that they expect to benefit from the attention.

“We welcome Dan Brown doing his work because Masonry has not had the kind of popularity that it once did and that a work by somebody of Dan Brown’s caliber could really attract people to Masonry,” Carter says.

The Freemasons date back to the Middle Ages, to associations of workmen who built cathedrals in Britain, though some also believe in a connection to ancient times with the mines where King Solomon took material for his Temple. Freemasonry has endured, and transformed. The British began to accept members who were not stonemasons and by the 1700s, lodges were being called “speculative,” philosophical societies rather than worker guilds.

The Masons, Crociata and others emphasize, are not a political or religious organization. No theology beyond the belief in a divine being is required and no causes are advocated beyond millions of dollars in annual contributions to children’s hospitals, cancer wards and other charities.

“This is the world’s oldest fraternity and it has an old and distinguished history,” Crociata says. “There’s much beauty to be found in its ritual. On the other hand, it’s a fraternity, not a religion. It’s a place to get together with guys that you know, that you trust, that you are willing to trust. A place where you can speak from the heart, if you want.”

No official gathering is taking place at the hall on this recent afternoon, so it’s all right for a reporter to have a look around. The Naval Masonic room has features common to other lodges, such as the Mason emblem, a set square and compass and letter “G” (for both God and Geometry), and some decorative images, such as the Egyptian-styled eyes and snakes painted throughout.

Brown’s book moves quickly among such Washington landmarks as the Library of Congress and the Washington Monument and draws upon the Masons’ very public presence in Washington, dating back more than 200 years.

George Washington used a Masonic gavel and trowel in 1793 as he lay the cornerstone of the U.S. Capitol. The same trowel would be included 55 years later when President James K. Polk, a Mason, presided over the laying of the cornerstone of the Washington Monument, and again in 1907 when President Theodore Roosevelt, also a Mason, laid a cornerstone for a Masonic temple.

According to “Freemasons for Dummies” author Christopher Hodapp (his book is so well regarded at the Naval lodge in Washington that it’s kept in a glass cabinet outside the meeting room), membership peaked in the United States just after World War II, when there were close to 5 million Masons.

The number dropped in the 1960s, when the Masons seemed hopelessly antiquated to a rebellious generation, and dropped again in the late 1980s as older members died. Hodapp, himself a Mason based in Indianapolis, says there are now around 1.5 million in the U.S. and 3 million worldwide.

“But it’s picking up again, in part because of people like Brown and (novelist) Brad Meltzer (‘Book of Lies,’ ‘Book of Fate’). Younger men are seeing popular references to it. We’re also seeing people from single-parent households who don’t have that kind of brotherhood feeling you get in the lodge,” Hodapp says.

Meetings at the Naval Masonic room are presided over by a Master who sits in a high-backed chair on the East side of the room, in honor of where the sun rises. On the South and West are chairs for the top aides, the senior warden and the junior warden. Only the North, “a place of Masonic darkness” (a belief related to the lighting of Solomon’s Temple) is not represented.

Every lodge has an altar on which is placed a holy book, or books. A Bible is usually there, but because only a belief in a higher being is required, a Quran or other religious text might be found, depending on the religious faith of the members present. The black and white squares of the checkered floor below the altar represent “good” and “evil,” terms the Masons resist defining too closely.

“As far as what is good and bad for any individual … the idea is to inspire thought on some of the important questions of life on the minds of our members so that they can go home and think about them and draw their own conclusions,” Crociata says.

Would-be members pass through three degrees of acceptance: Entered Apprentice, Fellow Craft and Master Mason. In “The Lost Symbol,” Brown describes an initiation ceremony that Hodapp says is essentially accurate. A man is blindfolded, has a dagger pressed against his chest and is instructed to vow that, “uninfluenced by mercenary or any other unworthy motive,” he will offer himself as “a candidate for the mysteries and privileges of this brotherhood.”

Brown is not a Mason, but said that working on the novel helped him imagine a time when religious prejudice would disappear and added that he found the Masonic philosophy a “beautiful blueprint for human spirituality.”

He was tempted to join, but, “If you join the Masons you take a vow of secrecy. I could not have written this book if I were a Mason,” he says.

And now?

“They’ve let me know the door is always open.”