This morning, word came that Harper Lee, the author of “To Kill a Mockingbird,” had died, at the age of eighty-nine. Lee was one of the most important and one of the most mysterious figures in American literary history. “To Kill a Mockingbird,” which won the Pulitzer Prize in 1960, became, for many readers, one of the key novels about race in America. (The film version, starring Gregory Peck as Atticus Finch, is an equally immovable cultural touchstone.) And yet, despite her success, Lee lived in relative seclusion, in her home town of Monroeville, Alabama. She didn’t publish another novel until last year, when “Go Set a Watchman,” a prequel to “Mockingbird,” appeared. In a review of that novel, Adam Gopnik considered the “extraordinary hold” that “Mockingbird” has on our collective imagination. It wasn’t just that the book treated race in an unusually incisive way, he wrote; readers treasured it for “the intensity of [its] evocation of coming of age, and of the feel of streets and summers at that moment. Harper Lee did for Maycomb (her poeticized version of her home town, Monroeville, Alabama) what J. D. Salinger did for Central Park—made it a permanent amphitheatre of American adolescence.”