‘The Mockingbird Next Door’ by Marja Mills

The publicity-shy Harper Lee, known as Nelle to intimates, granted the author rare extended access to her day-to-day life.Donald Uhrbrock//Time Life Pictures/Getty Images/File 1961/Getty Image

When she knocked at the modest home shared by Harper Lee and her older sister, Alice, Chicago Tribune reporter Marja Mills fully expected to be turned away.

In 2001, the Chicago Public Library was kicking off its “One Book, One Chicago” program with Lee’s 1960 Pulitzer Prize-winning classic, “To Kill a Mockingbird,” and Mills had been dispatched to Monroeville, Ala., to profile its elusive author.

Lee’s semi-autobiographical tale of a courageous defense attorney, a black defendant, and childhood innocence lost in 1930s Alabama had sold millions of copies, and its movie adaptation, starring Gregory Peck, had won three Academy Awards. But Lee, who split her time between Monroeville and New York City, never published another book, shunned reporters and biographers, and encouraged her close associates not to talk to outsiders.

Nevertheless, when Mills knocked and rang the doorbell, Alice Lee invited her inside. Still practicing law at 89 (and for a decade or so afterward), she was voluble and friendly. Later, she would encourage Nelle, as Harper Lee was known to intimates, to telephone Mills and drop by her hotel for an off-the-record chat.

After Mills’s story was published, an unlikely friendship developed. With the Lees’ enthusiastic support, the reporter rented a house next door in 2004 and, for about 18 months, shared their homely routines. The result, “The Mockingbird Next Door,” could be described as an authorized memoir — a rare, surprising, and respectful look at the Lees and their milieu.

Why did the Lees and their friends, who ranged from a retired hairdresser to a Methodist pastor and a onetime bank president, trust Mills? It’s clear that the reporter didn’t push too hard, that she knew how to blend in and when to beat a strategic retreat. Her own chronic lupus also made her sympathetic and vulnerable. “Beyond a shared passion for stories, for learning, it turned out that I had an awful lot in common with this gray-haired crew,” Mills explains. “Their joints hurt, too. They didn’t have the energy they once had either . . . These were my people.”

Mills accompanied the sisters as they drove rural roads, fed ducks, ate hearty Southern meals, watched college football, took exercise classes, sheltered from a hurricane, visited the laundromat. The book captures both the texture of Southern small-town life and the characters of the two Lees: Alice, orderly and precise, and Nelle, independent and feisty.

Alice regaled Mills with family history, while Nelle would telephone in the morning and say, “Hi, hon. You pourin’?” — the signal for Mills to put on a pot of coffee. “As disciplined as Alice was in her personal habits and routines,” Mills writes, “Nelle was a woman of appetites. It was part of what was appealing about her; her gusto for experiences and spirited debate and food.” Both sisters were bookish, hopeless at technology, and accustomed to living life on their own terms.

Mills was there, firing up the VCR, when two feature films about Truman Capote, Nelle’s childhood friend, were released. Nelle, who had helped Capote research his true-crime classic “In Cold Blood,” figured as a character in both. Their relationship had later soured. “Truman was a psychopath, honey,” Nelle tells Mills, in one of the memoir’s more startling moments.

Mills seems not to have pressed Nelle directly about why she didn’t publish a second book. Her sister Alice and her friend Tom Butts, the Methodist minister, suggested that the “the difficulty of living up to impossible expectations” created by her bestseller loomed large. Nelle had also talked of wanting to avoid “the pressure and publicity” and her sense that she had already said her piece.

“The Mockingbird Next Door” is an exceedingly polite book. It sheds no light, for instance, on the strange legal battle between Harper Lee (who had a stroke in February 2007 and is now 88) and a literary agent, Sam Pinkus, to whom she had, at one point, assigned her novel’s copyright (since returned to her). The suit, detailed in the August 2013 issue of Vanity Fair, was settled last year.

In 2011, The New York Times reported that Harper Lee was denying that she had cooperated with Mills’s book. Mills produced a statement by Alice Lee to the contrary, and “The Mockingbird Next Door” makes her case. Still, the renunciation seems a sad denouement to an otherwise charmed relationship.