“Mockingbirds sing sweetly and can mimic dozens of other birds,” Marja Mills writes in The Mockingbird Next Door: Life With Harper Lee. “They are tough, too, however, and don’t take kindly to other birds infringing on their territory. There’s something strong but also vulnerable about mockingbirds; those qualities applied to the one in the tree as well as the ones living in the modest brick house next door to the similar one I was renting.”

Mills, then a Chicago Tribune reporter on disability leave, moved to Monroeville, Alabama, in 2004 for just over a year and rented an apartment two doors down from Lee, the renowned yet reclusive author of To Kill a Mockingbird, and her older sister, Alice. After unexpectedly gaining access to Lee (“Nelle” to those close to her) back in 2002, Mills had published an article in the Tribune; Lee assigned it a “B plus,” telling friends that Mills is “a contradiction . . . a class-act journalist.” The book that resulted from their association offers a rare, not altogether satisfying account of the life of a woman who wrote one of America’s most beloved novels.

When Mills arrives in Monroeville, Lee is in her late 70s and is quick-witted, prickly, a practicing Methodist who’s culturally southern yet cosmopolitan. She likes fiction and nonfiction about the south, classical music, Christopher Guest movies, feeding the ducks, and fishing. And she still spends part of the year in New York City.

Mills is too enthralled with—and possibly intimidated by—Lee to critique her. But the reporter retains an eye for inconsistencies; she notes, for instance, that her subject’s disdain for New Journalism is odd given Lee’s pivotal work helping her friend, fellow Alabamian, and former neighbor Truman Capote research In Cold Blood. “Even more than a private author such as Nelle, these were people who had no chance to protect their private lives from what others might write,” observes Mills of the murder victims in Capote’s book.

Lee, who suffered a stroke in ’07 and moved to an assisted living center, hasn’t given a major interview to a journalist aside from Mills since 1964, four years after the publication of To Kill a Mockingbird. She’s touchy about the revered work’s image; just last month a federal judge dismissed a lawsuit she filed against an Alabama museum for trying to “capitalize on the fame” of the novel. Lee may even have a problem with The Mockingbird Next Door: in April 2011, she issued a statement in which she denied participating in or authorizing the book—a point Mills fails to note.

Including some of that behind-the-scenes drama might have benefited Mills’s book, in which nothing much happens and the few high points convey little more than a certain low-key southern charm. The author acquits herself reasonably well, but beyond the initial thrill of uncovering a famously reclusive subject, Mills’s Mockingbird sings a sweet, empty song.