In 1956, a 30-year-old airline ticket agent in New York was given what might well be the most significant Christmas present in literary history. From her friends Michael and Joy Brown, Nelle Lee received an envelope containing a generous cheque and the words, "You have one year off from your job to write whatever you please".
Within two months, Lee had the first draft of a novel based on her home background in Monroeville, Alabama. Over three years and several drafts later, it was published under the title To Kill a Mockingbird - by which time she'd replaced her first name (on the grounds that "most people call it 'Nellie'") with her middle name, Harper. The result, of course, was one of the most-loved and bestselling books in all American fiction.
So, wondered the world - and Lee's publishers - what would she write next? The answer, famously, was nothing. Very occasionally, she acknowledged the fact with rueful comedy: "I never read anything by you except To Kill a Mockingbird," a young girl once said to her. "Nobody else has either," Lee replied. Mostly, though, everybody who knew her understood that one thing you never asked Harper Lee was a breezy "and what are you working on now?"
In this gripping but always judicious book, Cep convincingly rejects the widespread idea that Lee (who died in 2016) was a recluse. In New York, where she continued to live and socialise, her name was on the doorbell of her apartment. When visiting Alabama, she happily hung out in local cafés. Even so, she gave no interviews after 1964, reluctant either to talk about "The Bird" - as she wearily called it - or face questions about its non-existent successor. She also took to the bottle. But while that can't have helped, the main reason for her spectacularly prolonged silence seems to have been that The Bird was simply too hard an act to follow. Its overwhelming success, she told that 1964 interviewer, was like "being hit over the head" and left her in a state of "sheer numbness". "Harper Lee thrives," she later lamented, "but at the expense of Nelle."
Then, in 1977, Lee heard of a trial in rural Alabama that might provide her with the material for a new book. Since 1970, two of the wives and three other relatives of a black preacher named Willie Maxwell had died in mysterious circumstances - perhaps made slightly less mysterious by the fact he collected huge sums in life insurance on all of them. The locals suspected voodoo. The insurance companies suspected something less supernatural but, unable to prove any wrongdoing, were forced to pay out anyway - usually by Maxwell's lawyer Tom Radney, one of Alabama's rare white liberals.
The last mysterious death was of Maxwell's 16-year-old stepdaughter, whose funeral attracted 300 mourners. At the end of it, one of them - Robert Burns, a relative of the dead girl - pulled out a gun and shot Maxwell in the head. Given that there were 300 witnesses, the prosecution were understandably confident of a murder conviction when the case came to court. Burns's lawyer, however, was none other than Tom Radney, who opted to turn the trial into a kind of referendum as to whether his former client had had it coming.
Cep persuasively argues that the appeal of all this to Lee went well beyond that of a cracking story. For one thing, Lee strongly objected to the many liberties her childhood friend Truman Capote had taken with the truth in his 1966 true-crime book In Cold Blood, which she'd helped to research. Now the Maxwell case gave her a chance to take a more honourable approach.
More intriguingly, suggests Cep, it also gave her a chance to correct something else that had long niggled her. In 2015, there was worldwide excitement at the much-hyped appearance of a "new" Harper Lee novel, Go Set a Watchman - followed by worldwide indignation that it was merely that first 1957 draft of To Kill a Mockingbird. The consensus was that this showed how good her editor, Tay Hohoff, had been. But there was also the troubling fact that everybody's favourite dad, Atticus Finch, was presented as far less unequivocally noble.
Back in 1957, this was among Hohoff's objections to the original version: that readers wouldn't buy the idea of a white lawyer who loathed the Ku Klux Klan and was willing to defend black people - but still opposed racial integration. Likewise, in 1961, Lee's only other fiction submission, the short story 'Dress Rehearsal', was rejected by Esquire magazine, which apparently felt that white segregationists who hated the Klan were "an axiomatic impossibility". "According to those lights," protested Lee unavailingly, "nine-tenths of the South is an axiomatic impossibility". Now, Cep claims, in Radney she had "the sort of morally complex character Tay Hohoff had encouraged her to avoid".
A reinvigorated Lee spent a year investigating the case and attending the trial, and several more working through the material she collected. Yet, as far as we know, the book was never written. Again, a combination of booze and the pressure of following you-know-what played its part. But there was also the sheer difficulty of getting at the truth she'd pledged herself to reveal, or even of organising all that she'd discovered into a coherent narrative.
Cep, faced with similar challenges, meets with rather more success. On the question of revealing exactly what Maxwell did, she sensibly sticks with explaining the impossibility of ever knowing. On the organising of the material, she clearly shares some of Lee's struggles, but in the end comes up with the required trade-offs.
So it is that Furious Hours begins with a section on Maxwell's life and crimes, then backtracks for an overview of Radney's career, before turning to Lee only about halfway through. It also pauses regularly to provide the background information we may or may not need.
Luckily, although some overall narrative momentum is lost, almost every individual part of the book rattles along compulsively. As well as the enthralling central story, there's plenty of great stuff on the always eye-popping business of southern politics. And perhaps best of all, Furious Hours triumphantly rescues Harper Lee from the myth she's been in danger of disappearing into - and restores her to full and recognisable human life.