Every now and then when it seems the world can’t get any greedier or immoral, a book comes along to remind us that the world’s always seemed spiritually bankrupt to the generations who lived through their own mad, bad times. That’s the implied premise of Southampton writer and historian Mary Cummings’ fascinating narrative about New York’s Gilded Age, which she revisits by way of one of the most bizarre murders in American history and its judicial aftermath, often called “the trial of the century.” At least before O.J. The date was June 25, 1906, when the debauched, unstable 35-year-old Harry K. Thaw coolly marched up to the celebrated and degenerate 53-year-old American architect Stanford White at White’s Madison Square Garden Tower club and shot him dead in front of hundreds of witnesses. The cause was young Evelyn Nesbit, chorus girl / artists’ model / actress, whom the infatuated architect and social lion had regaled with gifts, champagne and parties when she was 16, and deflowered