Harper Lee remains a landmark figure in the American canon -- thanks to Scout, Jem, Atticus, and the other indelible characters in her Pulitzer-winning debut, To Kill a Mockingbird; as well as for the darker, late-'50s version of small-town Alabama that emerged in Go Set a Watchman, her only other novel, published in 2015 after its rediscovery. Less remembered, until now, however, is Harper Lee the dogged young writer, who crafted stories in hopes...