Well, it's not a joke any more. The typescript was found by Carter late last year, in a safety deposit box kept by Lee's older sister, Alice. The manuscript of To Kill A Mockingbird had been kept there for years, but no one had thought to look at it more closely. When Carter began to leaf through it, she found another book attached to the back of that one: it contained many of the same characters - Scout and Atticus, of course - but they were older, and it was set in the late 1950s, when it was written, rather than in the 30s. She went to see her friend and client, Nelle Harper Lee, and revealed what she'd found.
"It's called Go Tell A Watchman," Carter reportedly told her.
Lee, apparently, didn't miss a beat. "You mean, Go SET A Watchman," she corrected her. (The line is a quote from the Bible - Isaiah 21:6.)
"I've started reading it," Carter went on. "It's a sequel to Mockingbird."
"It's not a sequel," Lee replied. "It's the parent."
Her genealogical terminology was precise: though To Kill A Mockingbird has an earlier setting, it grew out of Go Set A Watchman.
Naturally, there has been some scepticism. Lee is deaf and nearly blind and has lived in sheltered accommodation since she had a stroke in 2007; is she really of sound enough mind to have granted permission for the book's publication? The question may be immaterial since Carter appears to have power of attorney.
Go Set A Watchman seems likely to change the way we think about To Kill A Mockingbird for good. The main concern appears to be the truth about a cherished hero. To Kill A Mockingbird, a linchpin of 20th-century literature, has many subjects: childhood, racism, rape, reclusiveness, community, the American South. But at its core is the moral education of a young girl as she observes her exceptional father. The wise, funny, pared-down voice of the narrator, Scout, is what carries the book. But its hero, really, is her father Atticus Finch, a lawyer who takes on the case of a black man accused of raping a poor white woman. Though the jury convicts his client, Atticus is revered in the black community - as he has been revered in American culture ever since.
Go Set A Watchman takes place 20 years after To Kill A Mockingbird. Scout is 26. "Because it is seen through the eyes of an adult and not through the eyes of a child," Nurnberg explains, "things are much more nuanced. This was a very difficult time for people in the South, and people would veer from one position to another during those times of segregation." Or, as Arthur puts it: "If you scratch under the surface, those you thought were progressive are less progressive than you might imagine."
Harper Lee moved to New York from Monroeville, Alabama, in 1949. She had graduated from university but ditched law school with only one semester remaining. "She never intended to practise law," her sister Alice later said. But she "thought the disciplines of law were good training for somebody writing". Her father was a lawyer - the person on whom she based Atticus Finch - and so was Alice.
In New York, Lee took a job as a ticket agent with an airline - the British Overseas Air Corporation - because employees could fly to Britain at a discount. (She had spent the previous summer in Oxford, attending lectures given by C.S. Lewis, and she had, her sister later said, fallen in love with England.) She lived on the Upper East Side in an apartment without hot water, wrote stories late at night and occasionally met up with other Southerners. Eventually, her childhood friend, Truman Capote - who was partly brought up by relatives who lived next door to the Lees in Monroeville - introduced her to some of his cosmopolitan connections. He wrote to his friend, the songwriter Michael Brown, asking him to look after "a shy friend from Alabama".
Brown and his wife, Joy, took Lee under their wing. They recommended her to the husband-and-wife literary agents Annie Laurie Williams and Maurice Crain. An internal office memo dated November 28 1956 notes that "the author is a nice little Suth'n gal - from Alabama - who says 'Yes, Ma'am' and 'No, Ma'am'." Maurice Crain took her on, on the basis of five short stories. It's thought that at least one went on to become a scene in To Kill A Mockingbird; but none of them was ever published, and they haven't been found since.
That year, Lee spent Christmas in New York with the Browns. Michael Brown had just been paid for one of his "industrial musicals" - a genre in which he was commissioned by companies such as Singer and Electrolux to write paeans to their products - and the result was an act of generosity (or, as Lee later put it, "an act of love"). Lodged between the branches of the Christmas tree was an envelope with a note in it.
"Dear Nelle," it read, "You have one year off from your job to write whatever you please. Merry Christmas."
Lee got to work straight away; she wrote to a friend, with more prescience of doom than she could have bargained for: "I have a horrible feeling that this will be the making of me."
By January 14, 1957, she had delivered to her agent the first 50 pages of a novel. Maurice Crain noted his receipt of it on an index card headed with the names of the author and the book: "LEE, NELLE HARPER ... GO SET A WATCHMAN." A week later, she delivered the next 50 pages. The entire novel was delivered in 50-page batches, in sequence, with a regularity so precise that the system can only have been imposed by the author on herself.
The complete manuscript of 293 pages was in the agency's possession by the end of February. Crain worked on it with her for months, and sent it out to - as Joy Brown later recalled - 10 publishers who turned it down. But one publisher was interested: J.B. Lippincott, a family-run firm based in Philadelphia.
Lippincott - which had a New York office at 521 Fifth Ave - mainly published medical manuals, history textbooks and reading primers. There was only one female editor, Tay Hohoff, and she saw something in Lee's manuscript that she thought she could work with.
Lee visited the Lippincott offices that summer. Hohoff later described the occasion: "On a hot day in June 1957, a dark-haired, dark-eyed young woman walked shyly into our office on Fifth Avenue." But they didn't accept her book straight away. Crain's records reveal that Hohoff saw a new draft of Go Set A Watchman in July, and that it was revised again in August.
Finally, in mid-October, Lippincott signed a contract. Crain wrote to Lee, in a mock Southern voice: "Well, Honey, you done got yo'self a publisher!" Then he added: "It took a very bright woman editor to see the obvious."
But despite this triumph what followed was, in Lee's own words, "a long and hopeless period of writing the book over and over again". For the next two years, in New York and in Alabama, where Lee often returned to care for her sick father, she and Hohoff worked on the novel.
The book's title changed from Go Set A Watchman to Atticus to To Kill A Mockingbird. The author's name changed, too, as Lee decided to drop Nelle.
It's said that Hohoff encouraged Lee to focus on the flashbacks to Scout's childhood. It's also said they planned to publish To Kill A Mockingbird first, and the book set in a later period later, possibly with a bridging novel in between.
To Kill A Mockingbird is a novel about race, and it's easy to think, in retrospect, that Lee took on that topic when everyone was talking about it.
But the truth is that her position was exceptional, risky, and far ahead of its time. When Lee celebrated Christmas with the Browns, the year-long bus boycott led by Martin Luther King across her home state had only just ended. Though the Supreme Court ruled as a result that the segregation of buses was unconstitutional, that decision was followed by extreme racial violence. White Alabamans who opposed segregation were in severe danger: just four days before Lee delivered the first pages of her manuscript to Crain, five black churches and the home of a liberal white pastor had been bombed.
And yet Lee's views were clear. During one of her visits home around that time, she wrote to a friend that she had turned down a date with a Presbyterian minister, because, "I don't trust myself to keep my mouth shut ... it will get out all over Monroeville that I am a member of the NAACP [National Association for the Advancement of Colored People], which God forbid."
In 1962, with the film about to open, a reporter asked Lee how it was likely to be received in the South. "I wondered the same thing when the book was published," she replied. "But the publisher said not to worry, because no one can read down there."
There is something brilliantly complicated about that line - the impeccable timing of the joke, the sly diss to the publisher, the apparent allegiance with the person asking the question, the fond chiding of her fellow Southerners, and the implied opposite meaning about them: a strong but slightly unplaceable sense of honour. Lee stopped giving interviews a year later.
Is Harper Lee a recluse, or simply someone who guards her privacy? Those who know her are keen to stress that, unlike J.D. Salinger, she has not hidden from the world; she has just refused interviews to the press. However, Salinger wrote and published several books. Lee never published anything again. Why?
The usual argument is that the storm of publicity, and the extraordinary ongoing sales, of To Kill A Mockingbird alarmed her. (It has, to date, sold more than 40 million copies.) She responded to the book's success with "sheer numbness", she later said. "It was like being hit over the head and knocked cold." She was hoping for "a quick and merciful death at the hands of reviewers", she added, and perhaps a little encouragement. Instead, she got something far more frightening.
Go Set A Watchman is out now.