Her name was Rosamond Pinchot: hailed as "The Loveliest Woman in America," she was a niece of Pennsylvania governor Gifford Pinchot; cousin to Edie Sedgwick; half sister of Mary Pinchot Meyer, JFK's lover; friend to Eleanor Roosevelt and Elizabeth Arden. At nineteen she was discovered aboard a cruise ship, at twenty-three she married the playboy scion of a political Boston family, but by thirty-three she was dead by her own hand.

Seventy years later, her granddaughter, a noted landscape architect, received Rosamond's diaries and embarked on a search to discover the real Rosamond...