In the introduction to her biography of Elinor Glyn, author Hilary A. Hallett acknowledges that one of the biggest challenges she faced in writing the book "was not to let [Glyn's] many fascinating friends—and the many places they traveled—carry away the narrative for too long." Among the most intriguing of the secondary characters who populate Glyn's story is her older sister Lucy, later known as Lucy Duff-Gordon following her marriage to her second husband. Most high-born women of the Edwardian period, however, would have known Glyn's sister simply as Lucile, after the high-fashion clothing line she founded as one of the era's most famous couturiers.

According to Hallett's book, Glyn was, in fact, partially responsible for the launch of Lucy's career, after Lucy designed the gown her sister wore for her presentation at court, and later the costumes for a play in which Glyn starred. Soon Lucy's services were in demand, and she counted among her clients many of the most...