While Freemasonry is often depicted as a mysterious and highly secretive fraternal organization that has existed in the shadows of U.S. history since before the time of the Founding Fathers, artist Peter Waddell said his initiation into the world of American Free and Accepted Masons began with a simple knock on the door.

Waddell, a native New Zealander who gained his U.S. citizenship just two years ago, said that one day after he first came to Washington, D.C., and was looking around the city, he was taken aback by the mystical beauty of the House of the Temple — the striking edifice at the corner of 16th and S streets Northwest that serves as the headquarters of the Scottish Rite of Freemasonry.

And while most passersby simply gawk at the mausoleum-like building before moving on, Waddell knocked on the front door and asked to look around.

Little did Waddell know then that years later the magnificent interior of that striking building would become the centerpiece of a 21-painting exhibition titled “The Initiated Eye: Secrets, Symbols, Freemasonry and the Architecture of Washington, D.C.,” which opens Tuesday at the Octagon Museum.

As he walked among his finished pieces last week in the Octagon’s second-floor gallery, Waddell said that his original visit to the House of the Temple — which was designed by renowned architect John Russell Pope in the early 20th century — made him appreciate the lesser-known history of the building so much that it inspired him to seek out and learn about other Masonic buildings in and around the city.

As a history painter by trade, Waddell — who said his grandfather was a Freemason in New Zealand but insisted that he himself is not a Mason — decided that the beauty of Washington’s Masonic buildings along with the vast influence the group has had on the architecture of the District would make an intriguing study. He took the idea to the Octagon Museum, which in 2002 displayed his “Inside the Temple of Liberty: Nineteenth-Century Interiors of the U.S. Capitol” exhibit, and was eventually put in touch with members of the Grand Lodge of Free and Accepted Masons of the District of Columbia. To Waddell’s surprise, the group embraced his idea and threw open its doors to his research effort.

“I really had fantastic advisers, and they were extremely frank with me,” Waddell said. “They would answer just about any question, although there were some things that I didn’t ask and didn’t want to know because they weren’t part of the exhibition.”

After two years of intense study and countless hours of painstaking brush work, Waddell has brought to life 21 vivid scenes that, taken together, tell a large part of the story of the Masons’ influence on the Federal City.

“What Peter does is so unique when it comes to the mainstream art world, he creates these past scenes,” said Linnea Hamer, curatorial coordinator for the Octagon. “It just fits well with what a history-based museum like the Octagon does. It’s a unique way of presenting history because we don’t have photographs or paintings of what happened at some of those events, so he can kind of create those, he can channel history.”

And Waddell’s timing for his exhibition couldn’t be better. With the 2004 blockbuster film “National Treasure” prominently featuring American Freemasons and bestselling author Dan Brown’s upcoming book set to take place in D.C. and explore the mysterious group, public interest in Masonic imagery is at a peak not experienced in decades.

Waddell’s artistic journey begins at Thomas Jefferson’s Monticello where, in “The Age of Reason Made Manifest,” the history painter allows his viewers to lean over the great president’s dining room table and inspect a version of Pierre L’Enfant’s plan for Washington, D.C. That plan includes a street design that clearly incorporates the compass and the square — important Masonic symbols — in the city’s original layout.

Like every piece in the exhibit, the painting is full of symbolism, both explicit and more hidden.

“The exhibition has to work on a number of levels so that when the public comes they gain something from it, but I also tried to do it so that when Freemasons come they’re reading a subtext that isn’t immediately noticeable,” Waddell said.

For instance, in “An Auspicious Day,” a portrait painting of George Washington dressed in full Masonic regalia, the viewer might immediately notice the small model of the U.S. Capitol — which Washington laid the cornerstone for — in an open drawer at the president’s left. However, it might take repeated viewings before one picks up on the pattern of Masonic symbols Waddell has worked into the wallpaper behind the president.

As visitors move through the exhibit they will not only be introduced to Waddell’s unique mixture of artistry and history, but also a variety of Masonic artifacts, including three silver cups used in the ceremony at the laying of the cornerstone of the Washington monument, which have been loaned to the Octagon by Freemason lodges around Washington. Many of these artifacts are incorporated into the scenes Waddell helps bring to life.

In “Within These Walls,” the visitor joins President Harry Truman on one of his many late-night tours of the reconstruction work that took place at the White House in 1952. Truman, a Mason himself, used to enjoy exploring the gutted White House and examining the original stones that were a part of the building.

“He noticed while he was walking around that some of the stones had strange marks on them that he identified as the marks of the Freemasons who built the White House,” Waddell explained. “So what he did was he removed those stones with the marks on them and sent them around to various Grandlodges around the country, and we’re going to have two of those stones here for the exhibition.”

Along with showing the paintings and artifacts, the Octagon is also planning a series of lectures, gallery talks, walking tours and bus tours to bring to life the vibrant history of Freemasonry in Washington.

“I want people to realize that Washington is really an extraordinary city that is full of surprises and full of secrets,” Waddell said. “My idea is that we can initiate people who come to see the exhibition to a certain extent and they’ll understand Washington better. … I want people to realize that everything isn’t quite as it seems, which I think is very exciting.”

“The Initiated Eye: Secrets, Symbols, Freemasonry and the Architecture of Washington, D.C.” will be on display until Dec. 31 at the Octagon Museum, 1799 New York Ave. NW. For program dates and times, call (202) 879-7766.