At the end of the profile that Harper Lee wrote of Truman Capote when he published In Cold Blood, she speculated that “Kansans will spend the rest of their days at the tantalizing game of discovering Truman.” It was an odd claim; Capote loved publicity so much that even before he died, there was little left to discover about his time in Kansas, or anywhere else. Lee, by contrast, was so elusive that even her mysteries have mysteries: not only what she wrote, but how; not only when she stopped, but why.

For seventeen years after the publication of To Kill a Mockingbird, readers wondered what Lee would write next. In the years during and after she knocked on doors around Lake Martin, some knew exactly what but wondered when. Many people knew the title. One woman claimed to have seen a book jacket. Big Tom had heard from Lee more than once that the book was on its way to the publisher or that the galleys were already back from the printer. A friend of his remembered Lee saying, one night at dinner, that she had written most of it but was having trouble figuring out an ending. A friend of Lee’s in New York had a letter from her in which she said she’d written two-thirds of it before giving up. Someone claimed Louise had read the whole thing at her kitchen table in Eufaula and declared it better than In Cold Blood. An English professor at the University of Alabama heard from Lee’s old friend Jim McMillan that she had written the whole book but her publisher had rejected it because it was “too sensitive a subject.” McMillan’s daughter had heard it was all written, too, but locked away in a trunk, and would not be published until after Lee died.

Lee had arrived in Alexander City with such enthusiasm and chased her story with such determination that publication of The Reverend seemed imminent, but her second book, like the Second Coming, appeared to be delayed. She spent years working on The Reverend, some of them under the watchful eye of her sisterly Cerberus in Eufaula. Three years after that stint in Barbour County, her new literary agent, Julie Fallowfield, said, “It’s my understanding Miss Lee is always working.” Nine years later, Fallowfield told another reporter the same thing: “She’s always working on something.”

That Harper Lee was always writing was obvious to anyone who knew her, if only because they were reminded whenever they opened their mail. Lee’s correspondence constitutes its own archive, not only of her life, the heres and theres and sometimes the nowheres of her adventures, but also of her mind. She might have struggled sometimes with the prose in her books, but in her letters she wrote with the ear of Eudora Welty, the eye of Walker Evans, the precision of John Donne, the wit of Dorothy Parker, and, often, the length of George Eliot. Those letters came and went from friends and family around the country, while admirers and students around the world were thrilled to receive mail in response to their own.

Among other things, these letters revealed that Lee, a fan of small-stakes gambling, was a withering casino critic (“the worst punishment God can devise for this sinner is to make her spirit reside eternally at the Trump Taj Mahal in Atlantic City,” she wrote to one friend in 1990), a capable sportscaster (ESPN could have hired her solely on the basis of her 1963 report on the “lallapalooza” that ensued when Wally Butts and Bear Bryant were accused of fixing a Georgia-Alabama football game), a dedicated chronicler of bar ballads from around the world (including Thomas Hardy’s favorite, “Come Where the Booze Is Cheaper,” with its rousing call to “Come where the pots hold more! Come where the boss is a bit of a joss! Come to the pub next door!”), and an amusingly sympathetic homicide reporter (“I know exactly why she did it,” she explained in 1976 of Lizzie Borden: “Anyone burdened with long petticoats and having had mutton soup for breakfast on a day like that was bound to have murdered somebody before sundown”). Her letters were even known to include appendixes, some of them in verse. She once sent a friend in New York an Edward Lear–like guide titled “Some Sociological Aspects of Peculiarities of Pronunciation Found in Persons from Alabama Who Read a Great Deal to Themselves.” After explaining how she came by her short e’s and soft c’s, she jests, “I was quite correct in every respect, down to wearing goloshes when rainy, / But was looked at askance—like I’d left off my pants—when I ventured to speak of Dunsany.” (Forever a fan of Shakespeare, she’d been horrified in her younger days to have once mangled that place name from Macbeth.) The couplets go on like that for nearly a page, getting funnier at every line but suggesting her chronic failure to fit in, even where she should have: “For in this city the learned and the witty cannot be exactly called snobs— / It’s not how you dresses but the fall of your stresses that tells the Brows from the slobs!”

Lee’s writing voice catches like a briar; it doesn’t tear its subjects, but sticks to them. Both her extensive field dispatches on life in Monroeville and Manhattan and her brief forays into journalism make it clear that Harper Lee could write nonfiction as ably as fiction. What she was writing, though, was always anybody’s guess. “She continued to write,” her sister Alice said of Nelle’s work in the decades after Mockingbird. “I think she was just working on short things with an idea of incorporating them into something. She didn’t talk too much about it.”

Whatever she was writing, Harper Lee wasn’t publishing any of it, but no wonder can be dismissed as one hit right away. It takes the passage of time for such language to feel applicable, and even then it is a strange and varied category, especially for writers of fiction. Lee wasn’t like Napoleon or Mussolini, whose single novels came early but were eclipsed by other pursuits, and she wasn’t like J. D. Salinger, whose one novel was accompanied by stories and novellas, or like Oscar Wilde, whose one novel hid in a thicket of plays, or like Dorothy Day and Thomas Merton, whose novels were but worldly pauses on their saintly processions, or like Lionel Trilling and Harold Bloom, who could be excused for just trying to practice what they preached in the one novel each that accompanied all of their literary criticism, or even like Emily Brontë and other literary wunderkinds who might well have produced additional novels had they not died first.

No, Lee wasn’t like any of those. She was at some point, and then forever after, put in the same literary bushel basket as Margaret Mitchell and Ralph Ellison, who published wildly successful first novels but then were never heard from again. Ellison’s Invisible Man appeared in 1952, and he worked on a second, “symphonic” novel for over forty years, but when he died in 1994, all he left behind was two thousand pages of notes. Mitchell had been a client of Annie Laurie Williams’s and had won the Pulitzer Prize and the National Book Award for her first and only novel, an example that must have struck fear into Williams and Maurice Crain—Lee’s first literary agents—and possibly even into Lee herself once it was made known to her. Mitchell was killed in a car accident in 1949, but by then thirteen years had passed since Gone with the Wind. She, at least, had the excuse of “the jitters” brought on by World War II and her time volunteering with the Red Cross, not to mention pleurisy, eye problems, and a predilection for “the humbles,” her term for her awe of other writers. But while Mitchell offered excuses and Ellison offered pages, Lee rarely even pretended to offer either.

Writer’s block is a symptom, not a disease. It describes only the failure to write; it does not explain it.

Casey Cep is a writer from the Eastern Shore of Maryland. After graduating from Harvard University with a degree in English, she earned an M.Phil in theology at Oxford as a Rhodes Scholar. Her work has appeared in The New Yorker, the New York Times, and The New Republic, among other publications. Furious Hours is her first book.

Excerpted from Furious Hours, by Casey Cep. Copyright © 2019 by Casey N. Cep. Excerpted by permission of Alfred A. Knopf, a division of Penguin Random House LLC. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.