This is a love story. It involves a determined real estate developer, a sensitive architect, an inventive engineer, a thoughtful government official, a passel of talented craftspeople and a beautiful building -- Argyle House, the newly reborn chateaulike mansion that dominates the corner of Florida and Massachusetts avenues NW.

On Sept. 5, 1984 -- with a major renovation half-finished, the interior nearly all framed and mechanical and electrical systems well along -- Argyle House ignited in a spectacular blaze that required 150 firefighters working several hours to extinguish. The U.S. Treasury Department's Bureau of Alcohol, Tobacco and Firearms determined that the fire was set, but the arsonist has not been caught. Damages totaled about $2 million: The interior and roof were totally destroyed, and all that was left standing were parts of the masonry facade.

Today, however, the fully restored building, now converted to condominiums, looks as bright as it did when it was built 85 years ago.

The mansion was completed in 1901 to the design of Paul J. Pelz, associate architect of the Library of Congress. It was built as a single-family residence for a U.S. Navy commander, but since the Depression had served as a rooming house inhabited by some 35 transient boarders. Over the years, the once-grand rooms had been chopped up and the 11- to 12-foot ceilings reduced by the installation of lofts to permit sleeping areas for additional tenants. The result was, in the words of developer Bruce H. (Scott) MacLeod, a "rabbit warren." Still, the Argyle remained a neighborhood landmark.

Richard Ridley, architect of the renovation, sees dual significance in the Argyle. "The building is a precursor to Embassy Row," he declares. "It set the stage for the classical revival buildings up the street." Equally important, Ridley adds, is its location: As half of the gateway to Sheridan Circle, thousands of cars pass it daily.

MacLeod, an officer of the World Bank who describes renovation as his avocation, acquired the Argyle in 1983 as another in a string of a half-dozen similar projects he has taken on in the Dupont Circle area, each more difficult than the last. MacLeod undertakes these preservation projects in part, he says, because he "likes to play architect," but the complexity of the Argyle job mandated the use of a professional designer. In Richard Ridley he found what he was looking for, "an architect willing to give up his ego."

For his part, Ridley describes the task as "a puzzle. You have to figure out how to put the big rooms in the major spaces and not disrupt the original plan." The large bays serve as living rooms and master bedrooms. Starting with a pair of single-level units on the ground floor and duplexes above, the architects repeated that pattern on the upper three floors of the six-story structure. Showing off the spaces to a visitor, Ridley and his associate, Shawn G. Pierson, take justifiable pride in the way they were able to maintain a sense of volume within relatively compact areas.

In order to convert the mansion from a rooming house to condominiums, MacLeod had to seek some fairly routine exemptions to a number of zoning regulations. That process drew some neighborhood opposition he still has trouble comprehending. "One would think there would be universal support," he says, "since the density was being reduced, the building rehabbed and the clientele upgraded." Understandable concern was voiced about the impact on parking in such a congested area, but other criticism centered on the economically impractical notion that the building should have only two or three units instead of the nine MacLeod and Ridley had planned (eight in the building proper and another in the integral "automobile house," one of the district's first garages).

Eventually, MacLeod won support for his plan and construction started. Then came the devastating fire.

Immediately following the fire, because of the threat posed by the remaining broken sections of wall, the District government declared the property a danger to public safety and ordered that it be demolished or braced within 24 hours. The Argyle looked awful, and few believed it could be saved. But MacLeod was determined to do just that, a decision he admits was based in part on a philosophic commitment to preservation and in part on ignorance. "I didn't know what I could or could not do," he recalls, "and thus decided to keep my options open."

As a first step, MacLeod brought in Allyn E. Kilsheimer of KCE Structural Engineers. Working on the site, because of the time constraint, Kilsheimer devised a system of steel bracing that would keep the facades in place temporarily. While the method is not unlike that used all over this city when old building exteriors acquire newer and larger interiors, Kilsheimer did not have the benefit of several weeks or months to plan. Furthermore, he had to convince safety officials that his idea would work and that the dangerously tottering walls would hold while the structural frame was being installed.

There were a number of hindrances to progress, some bureaucractic and some architectural. For one thing, MacLeod says, the D.C. building permit office could not decide if the building was old or new and therefore which codes to follow. Another problem occurred because no work, except for minor maintenance, had originally been scheduled on the exterior, so the architects had had no need to draw the various elevations. After the fire, they had to re-create them from photos and on-site examination of pieces of the building that had fallen to the ground.

Designing the roof was an exceptionally difficult task, Ridley says, because of the unusual, complex curve shapes involved and the need to convert a wood frame to a steel one. The architect also notes that he and MacLeod wanted to add skylights to the ridge of the roof, citing as a precedent those at the Corcoran Gallery, but the National Park Service -- which would determine the project's eligibility for preservation tax credits, an important factor in marketing units purchased for investment -- vetoed the idea, saying the roof had to be identical with the original. (Well, almost identical: A slatelike mineral fiber shingle was allowed instead of real slate.) In the end, skylights were installed out of sight on the flat section of the roof.

The fire also raised a complicated philosophical problem that took some time to resolve. In a routine action following the fire, the Park Service staff withdrew the "certificate of significance" that had made the project eligible for the preservation tax credits. But after a hearing, the tax credits appeals officer, Ernest A. Connally, reinstated the certificate. He declared that because of the setting and location, among other factors, the Argyle had not lost its historic integrity. He also found that although the interior was destroyed, the basic form of the building had survived, as had the finest details.

The design and approvals process completed, reconstruction commenced. Matching Roman brick was made, but it was found that the bricks were too big and each had to have 1/8-inch cut off from one side. After much trial and error, a way was devised to recast the terra-cotta decorative elements (most of which had sea-inspired motifs, due to the original owner's profession) in an on-site workshop. Stonemasons were able to reconstruct the original elaborate window frames. Paneling from an old house was installed on the interior. Even the famous carved stone cat, which had stood on the Massachusetts Avenue cornice, was found in the rubble and returned to its perch.

That feline phoenix serves as a symbol of the Argyle's rebirth. Despite the fact that "it took time and money and a lot of aggravation," MacLeod believes "the final results are worth it." A large number of Washingtonians would agree.