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Christine Shaw said neighbors told her it had been “over 40 years” since there had been a party in the Shaws’North Shore mansion that came close to resembling the one she and her husband, Robert, a developer, hosted Friday night.

The unusual entertainment for the evening was a private operetta for about 100 guests, a genteel, monied mix of fine arts lovers and preservationists. They sipped champagne and nibbled appetizers in the Gatsby-like atmosphere of the legroom, Lake Forest house previously owned by Mr. T.

This was also the first formal party in the famous mansion for the Shaws, who have yet to move into “Two Gables” since their purchase of it last June. “We hope there will be many more cultural events here,” Christine Shaw said. The musical presentation featured baritone Lauri Vasar and soprano Elisabeth Kainz, two young Austrian singers here to make their public, American debut Sunday in an all-Mozart concert with the Ars Viva Symphony Orchestra at Skokie’s North Shore Center for the Performing Arts. On this night, the proceedings weren’t as formal.

Their breezy, 20-minute performance in which they were accompanied by pianist Richard Boldrey was a “Singspiel,” which, it was explained to guests, had centuries-old roots as light-hearted musical entertainment presented between acts of especially long, laborious operas in Germany and Austria. The storyline for Friday’s production, a domestic dispute over the husband’s drinking, was simple: his angry wife locks him out of the house. The lone prop was a door.

“This gives new meaning to minimalist staging,” said Alan Heatherington, Ars Viva music director, in his introduction. “Don’t worry. You won’t be asked to sing along.”

Vasar and Kainz later professed little knowledge of Shaw’s house being owned by the actor Mr. T., who, as the evening’s program noted, “once engaged in high-profile reduction of the historic landscape,” an ever-so-polite way of saying Mr. T chopped down more than 100 trees in a nationally reported story that made him the most famous lumberjack since Paul Bunyan.

The historic house, on 8.5 acres, was designed by famed architect Harrie T. Lindeberg and built in 1910.

The mansion’s original owner was broker Orville Babcock, a senior partner in a Chicago firm that traded on Wall Street and with the Chicago Board of Trade.

Babcock sold the house in 1913 to Laurance Armour, a president of several large Chicago banks whose uncle, Philip D. Armour, founded the meatpacking dynasty.

Laurance Armour died in 1952. His widow, Lacy, was the house’s last occupant before it was sold to Mr. T in 1986 by the estate.

The neighborhood through the years included the Louis Swifts, just up Green Bay Road a few blocks, as well as prominent lawyer Noble B. Judah, who served as an early U.S. ambassador to Cuba. Onwentsia Country Club, also designed by Lindeberg (he specialized in summer mansions favored by the elite), is just across Green Bay from “Two Gables.”

The Armours did much entertaining. In addition to being a horseman who played polo at Onwentsia (one of three country clubs he belonged to) and president of the Post & Paddock Club at Arlington Park, Laurance also was an officer with Chicago’s Grand Opera Club.

The party thrown by the Shaws was to help Ars Viva, a four-year-old fine arts orchestra and choir. (Christine Shaw is on the board.) But the singers, whether they knew it or not, shared top billing with the mansion. Right after the “Singspiel,” most guests toured all 16 rooms as well as the extra seven rooms once occupied by Armour servants.

The Shaws and their daughter, Rachel, don’t expect to move in for a while. Robert Shawsaid removing asbestos from the house was the first task, and now he is focusing on its plumbing. The house’s interior was left in good shape by Mr. T, whose biggest contribution appeared to be bright red carpeting and a bathroom in the same color.

When spring arrives, there is no question about the next priority. “We’ll be planting trees,” said Christine Shaw.