In February of 1901, Walter Berry, a lawyer and member of élite society in New York, expressed a regret in a letter written to his close friend Edith Wharton. “How I do wish I could run on to see the first rehearsal of the Shadow,” he wrote. At the time, Wharton, who was thirty-nine years old, was not yet a novelist, having only published shorter fiction and poetry, as well as co-authoring, with Ogden Codman, “The Decoration of Houses,” an 1897 book about interior design. But she was a budding playwright, and, as two scholars have just deduced in an...