Alice Mason was throwing one of her black-tie dinner parties. For years, she had been hosting events that New York City’s social pages fawned over, but she didn’t expect that this one would disrupt a secret she had kept for much of her life.

A Manhattan real estate agent to the elite, Alice typically held six dinner parties a year, almost always with 56 attendees — half women, half men, not too many couples. Her guests, as one socialite put it, were “the A-list of A-lists”: Barbara Walters, Bill Clinton, Gloria Vanderbilt, Alan Greenspan, Norman Mailer, Estée Lauder, Mary Tyler Moore, Jimmy Carter.