Author Harper Lee. (Chip Somodevilla/Getty Images)

After the Supreme Court issued its landmark 1954 decision in Brown v. Board of Education, declaring segregation in public schools unconstitutional, Robert Penn Warren set off on a journey south. He was returning to his native land from New York City to witness and contend with the effects of the ruling on its people: “I was going back to look at the landscapes and streets I had known,” he wrote, “to look at the faces, to hear the voices, to hear, in fact, the voices in my own blood.”

So, too, begins Harper Lee’s much-anticipated­ novel, “Go Set a Watchman,” with a grown-up Jean Louise Finch’s journey home from New York to visit her ailing father, Atticus Finch. This is also a journey undertaken in the wake of Brown, and not long after the two are reunited, her father asks: “How much of what’s going on down here gets into the newspapers?” — setting in motion one of the book’s guiding preoccupations.

Evidence suggests that “Watchman” was an early version of Lee’s Pulitzer Prize-winning 1960 novel, “To Kill a Mockingbird,” resubmitted after her publisher asked her to rewrite “Watchman” to focus on the perspective of Scout, a childhood version of Jean Louise, and place the story 20 years earlier, in the 1930s.

Reading “Watchman,” which publishes Tuesday, one sees the imprint of the earlier draft — whole passages repeated nearly word for word: descriptions of the fictional town of Maycomb, Ala.; character studies of its residents seemingly in preparation for the work it would become — all of this good fodder for scholars, writers and students of literature and writing who can measure in it the evolution of a writer and her story through the process of revision.

Although the novel covers at first some familiar ground with flashbacks, the momentum changes just over a third of the way through to focus on the crux of the contemporary story — contemporary in the era it was written — that we have not heard. Jean Louise is a grown-up tomboy contending with gender roles she is loath to accept, a would-be suitor, and a newfound disappointment with her father and his ideals rooted in the transformations wrought by adulthood and the burgeoning recognition of different worldviews.

The cover of Lee’s new book. (Harper Collins)

In “Mockingbird,” Atticus became a kind of national hero, a progressive thinker who espoused the noble belief in equal rights: “Gentlemen, if there’s one slogan in this world I believe, it is this: equal rights for all, special privileges for none.” In “Watchman,” written in the third person, Scout, thinking of her father, recalls “a tiny voice talking in the warm comfortable past.”

The adult Jean Louise encounters a different Atticus from what readers of “Mockingbird” will remember. He joined the Ku Klux Klan and attended one meeting and is now a board member in one of the newly formed Citizens’ Councils springing up in communities throughout the South to oppose desegregation, in “protest to the Court . . . a sort of warning to the Negroes for them not to be in such a hurry.” This is the harsh reality with which Jean Louise must contend. In prose less nuanced than that of “Mockingbird,” prose steeped in the political rhetoric after the Brown decision, the characters in “Watchman” carry out an ideological debate that began in the South but would come to occupy the national consciousness in the 1960s and 1970s and in many ways continues today.

There are some changes to the history of the Finch family that cause a rupture in the ongoing narrative for readers who know “Mockingbird”: the case of the black man, Tom Robinson, falsely accused of rape but found guilty nonetheless, is transmuted to become the case of a black man acquitted for sexual congress with a white woman — an encounter that was revealed to have been consensual. Thus, the case that made Atticus a household name synonymous with righteousness and justice for all — even as he lost — is undermined.

Now, instead of his sweeping and eloquent plea for the rights of all citizens, black and white, we encounter some of the novel’s most difficult passages: Atticus advocating for the preservation of segregation, the hierarchy of racial supremacy to which — despite what appears to her father’s generation, and to readers, as a kind of self-righteous, moralizing indignation — Jean Louise consents in large part: “We’ve agreed that they are backward, that they’re illiterate, that they’re dirty and comical and shiftless and no good, they’re infants and they’re stupid, some of them, but we haven’t agreed on one thing and we never will. You deny that they’re human.”

And herein lies the paradox at the heart of “Watchman” that many white Americans still cannot or will not comprehend: that one can at once believe in the ideal of “justice for all” — as Atticus once purported to — and yet maintain a deeply ingrained and unexamined notion of racial difference now based in culture as opposed to biology, a milder yet novel version of white supremacy manifest in, for example, racial profiling, unfair and predatory lending practices, disparate incarceration rates, residential and school segregation, discriminatory employment practices and medical racism.

The argument that enlivens “Watchman” is one rooted not only in the class distinctions between “good white people” and “trash,” originally articulated in “Mockingbird,” but also an argument among all white Southerners anxious about the tumultuous times of court-ordered desegregation and apprehensive about the future. The action by the court, and the federal government enforcing the court’s edict, is presented as an affront to the way things were, to the status quo — the warm, comfortable past — and the paternalism that allowed many Southern whites to love the negro as long as he stayed in his place. This is a white South trying to hold on to its rights — a troubling adherence to the uses of the doctrine of states’ rights — once to maintain the institution of slavery, later to maintain Jim Crow laws.

A deep disappointment runs through the heart of the novel as the Finch family struggles with personal conflicts brought on by the social upheaval of the 1950s South. If Atticus is not willing to accept desegregation, Jean Louise also is resistant to change and anxious about it, even as she knows it must occur. A significant aspect of this novel is that it asks us to see Atticus now not merely as a hero, a god, but as a flesh-and-blood man with shortcomings and moral failing, enabling us to see ourselves for all our complexities and contradictions.

“Watchman” is compelling in its timeliness. During the historical moment in which the novel takes place, in states such as Georgia and South Carolina, legislators had begun to authorize the raising of the Confederate flag over the statehouse or the incorporation of it into the design of state flags as a reaction and opposition to the Supreme Court’s decision — thus inscribing the kind of white Southern anxiety dramatized in Lee’s novel.

Perhaps the recent lowering of the Confederate flag on South Carolina’s statehouse grounds is a beginning — but there is still a long way to go. In the conclusion to his 1956 book, “Segregation: The Inner Conflict in the South,” Warren put it like this: “If the South is really able to face up to itself and its situation, it may achieve identity, moral identity. Then in a country where moral identity is hard to come by, the South, because it has had to deal concretely with a moral problem, may offer some leadership.”

Although there persists in “Watchman” an idea of the primacy of the individual conscience, the novel serves to remind us that we are at a moment in our ongoing pursuit of justice that puts our national conscience at stake, and it is all the more pressing that the watchman be attuned to the collective soul of our nation.

Perhaps the best thing about this book is that it gives us a way to look at history from a great distance. It has been 61 years since the Brown decision, and now we have the hindsight to see the larger impact that Lee’s characters could not quite see: an outcome, as Warren suggested — that “desegregation is just one small episode in the long effort for justice.”

Natasha Trethewey, a former U.S. poet laureate, is a professor at Emory University. She was awarded a Pulitzer Prize in 2007 for her collection “Native Guard.”