NEW YORK — On Wednesday, HarperCollins unveiled the jacket art for Harper Lee's "Go Set a Watchman," the unexpected follow-up to her classic "To Kill a Mockingbird." The new cover, like the one for "To Kill a Mockingbird," is a moody illustration featuring an oak tree in front, but also shows train tracks and a train in the distance. In a statement released by HarperCollins, company President Michael Morrison noted that "Go Set a Watchman" begins with "Mockingbird" protagonist Scout Finch returning by train 20 years later, in the 1950s, to her native Alabama.