It's been more than half a century since Lee's only other novel was published — the Pulitzer Prize-winning To Kill a Mockingbird. Her latest book, Go Set a Watchman, is a sequel set 20 years later, but was completed prior to Mockingbird.
Written in the third person, the novel follows the now grown-up Scout Finch on her return to Alabama from her home in New York to visit her father, 72-year old Atticus Finch.
Fans have already embraced the sequel by opening their wallets — it's the most pre-ordered book in publisher HarperCollins's history — but they've also been quick to react to pre-released snippets of Watchman.
The first chapter of the book was published online, and fans immediately expressed their surprise at the death of Scout Finch's older brother, Jem.
Then an unexpected early book review from the New York Times unveiled a darker side to the much-beloved Mockingbird character Atticus Finch.
It turns out the heroic and moral father and lawyer, who fought for a black man's rights after he was falsely accused of raping a white woman, is a racist.
In Watchman, he reportedly attends a Ku Klux Klan meeting and warns his daughter about "Negroes."
Fans have not taken Atticus Finch's fall from grace lightly and have shared their disappointment online.
Lawrence Hill, author of the The Book of Negroes, said he was "shocked" to learn Finch had turned from his once "saintly" character.
"It was a disturbing thing. But I'm not going to criticize Harper Lee for doing it. It was a brilliant decision novelistically," said Hill, who will also be reviewing the book.
Bahram Olfati, the senior vice-president for print at Indigo Books and Music, reminded fans to consider the era in which Watchman was written and set.
"She's describing a 72-year old man in 1950s America, prior to the civil rights," said Olfati. "We see racism today everywhere, so I'm not sure why people would get saddened that this character, in a time capsule of a book that was written last century, is a racist."
For years it was thought Lee's manuscript for Watchman was lost, but her lawyer made the surprise discovery supposedly last year. That date has been debated, with the New York Times reporting it may have been found as early as 2011.
The famously private Lee has poor hearing and vision and resides in an assisted living facility in her hometown of Monroeville, Ala. Questions have been raised as to whether she freely consented to Watchman being published.
Filmmaker Mary Murphy spent time with Lee's circle of friends and business contacts — and even briefly with the author herself — for her documentary Harper Lee: American Masters. Like Lee's lawyer and publishers, she believes the 89-year old is "unequivocally" delighted to be publishing the work.
"Harper Lee doesn't do anything that she doesn't want to," Murphy told CBC News. "Her written statements that were released have reflected pleasure and happiness at the publication of another book. Without asking her directly, that's as much as I know."
It's a stunning change of heart from an author who once said she would not be releasing any more of her writing after Mockingbird.
With only hours to go until Go Set a Watchman hits store shelves, it seems fans can expect even more twists and turns from their beloved author.