In the final pages of Colson Whitehead’s forceful and tightly wrought novel, Millie, new partner to the main character, recalls: “It was hard to remember sometimes how bad it used to be – bending to a colored fountain when she visited her family in Virginia, the immense exertion white people put into grinding them down – and then it all returned in a rush, set off by tiny things, like standing on a corner trying to hail a cab … [and] by the big things, a drive through a blighted neighborhood snuffed out by that same immense exertion, or another boy shot dead by a cop.”

When I first came to live in Virginia four years ago, friends made jokes, with raised eyebrows, about how we were moving “to the South”. I didn’t really worry, because to me Virginia didn’t seem particularly southerly. Virginia wasn’t Alabama, wasn’t Florida – the setting for Whitehead’s novel. Yet in Virginia, at the time of my birth, my parents (one white, one black) would have been forbidden to marry. Following Brown v Board of Education in 1954, Virginia successfully opposed desegregating schools for decades. A neighbour who lives in one of the older houses in the area told me that the deeds for his house contain a clause forbidding its sale to non-whites. “Unenforceable today,” he half smiled. His parents are immigrants from Pakistan.

On trips further south, to Mississippi, Tennessee and Florida itself, I started to ask people in their 70s and older – not black people, but white people – what it was like to grow up in the era of segregation. I was curious to know how it felt to be able to order a black person to the back of the bus, have black people step aside for you in the street, to always sit in the best seats in the cinema. Those privileges had been lost in living memory, and yet much of the US treats the issue of segregation as if it belongs to ancient history. I have had these conversations with white people in South Africa, and yet every single American I talked to claimed not to be able to remember. One man told me that the town where he had been raised had been a “progressive” sort of place, where these things didn’t happen. Shortly after our conversation the New York Times ran a spread about a lynching that had taken place there in 1935, before my interlocutor’s birth, but at a time when his parents certainly lived there. The victim’s name was Elwood Higginbotham.

Elwood is also the name of one of the protagonists of The Nickel Boys. Elwood Curtis grows up at the time of Brown v Board of Education, listening to the speeches of Martin Luther King and imbibing every word. Elwood’s grandmother Harriet, who is raising him, is less convinced; not of the need for civil rights, for she takes part in the bus boycott once she’s assured herself that everyone else is doing the same, but about sticking your head above the parapet. Whitehead has a gift for summarising the essence of a person’s nature in a few lines: “She kept a sugarcane machete under her pillow for intruders, and it was difficult for Elwood to think that the old woman was afraid of anything. But fear was her fuel.”

Elwood works hard and gets good grades, attracting the attention of a new teacher at his school, who is also a civil rights activist and gets him into free classes at a coloured college south of Tallahassee. Hitchhiking there, Elwood picks the wrong driver from whom to accept a ride: “When Rodney shook his hand, the rings on his fingers made Elwood wince.” Rodney is a car thief and soon the pair are pulled over by police. And through this one small error of judgment, Elwood’s life is changed when he is sent to a reform school called Nickel. There he is under the rule of superintendent Maynard Spencer, “who moved with a deliberate air, as if he rehearsed everything in front of a mirror … Spencer was fastidious with his dark blue Nickel uniform; every crease in his clothes looked sharp enough to cut, as if he were a living blade.”

According to Whitehead’s acknowledgments page, The Nickel Boys was inspired by the true story of the Arthur G Dozier School for Boys in the small panhandle town of Marianna in Florida. After numerous reports and finally an investigation, including the excavation of a number of unmarked graves by a team of archaeology students in 2012, NPR reported that some 81 boys had died there. Dozier only closed its doors in 2011, and many of its former inmates are still only in their 60s. Although Whitehead is clear that Nickel, the characters and their stories are fiction, he has been true to many of the details of the Dozier regime: the brutal night-time beatings, in which boys were snatched from their beds and taken to a place called the White House, and the killings.

And yet for all the horror, the descriptions of violence are remarkably understated. For the most part this restraint adds to the book’s impact, underlining the detachment with which the violence was enacted. There are other times, though, when Whitehead slides over key moments that would seem to beg for more detail: Elwood’s conviction and sentencing, for example (we skip from the moment of his arrest to his incarceration), and another scene which I can’t describe without spoiling the book, but which also left this reader wondering exactly how a seemingly inescapable moment unfolded. Instead of the violence, Whitehead homes in on the way in which every action fits into a fully orchestrated whole, which is why I would wish everyone, black or white, to read this novel. He demonstrates to superb effect how racism in America has long operated as a codified and sanctioned activity intended to enrich one group at the expense of another. Racism and white supremacy are the ideologies underpinning the economic exploitation of black people, once given legal force by Jim Crow laws. These laws put power into the hands of ordinary white people. A white person could have a black person arrested for “bumptious contact” – not giving way on the sidewalk, say. The system benefited ordinary white people, from the shopkeepers who resold the food supplies meant for the reform school boys, to the housewife who had her gazebo painted at no cost. Thus, ordinary white people were invested in sustaining the system, including what took place at schools like Nickel. For that was where black boys who did not submit early ended up.

Elwood’s best friend in Nickel is Turner, who seems to have learned the reality of survival faster than most. Turner was “simultaneously at home in whatever scene he found himself and also seemed like he shouldn’t have been there; inside and above at the same time; a part and apart. Like a tree trunk that falls across a creek – it doesn’t belong and then it’s never not been there, generating its own ripples in the larger current.” Turner is affable, artful, cunning and kind; a boy who might have enjoyed the freewheeling adventures of a Huck Finn, if only he hadn’t been born black. Turner isn’t interested in Dr King’s notion of how the world should work; instead, he is clear-eyed about how it does work and how it might work for him. At Nickel boys are supposed to be able to advance their release date through good behaviour, but nobody really knows how the system of merits and demerits works. With Turner’s help, Elwood figures out that all that really matters are the whims of the white person in charge. Nickel is a microcosm of a corrupt world, in which the rule of law is meaningless and the real laws are unwritten.

Last month the Washington Post reported a supreme court ruling that Mississippi prosecutors engaged in a “relentless and determined effort” to exclude African Americans from a jury considering the case of another African American (whose first name this time was coincidentally Curtis), thus denying him a fair trial. So far Curtis Flowers has been tried six times, going back to the 1990s.

“Their daddies taught them how to keep a slave in line, passed down this brutal heirloom,” writes Whitehead. “They waited for wayward boys in need of an attitude adjustment. They wait still, as long as the sons – and the sons of those sons – remember.” In the American south, for both black and white people, the memories and the wait go on.

• Aminatta Forna is the author of Happiness, published by Bloomsbury. The Nickel Boys is published by Fleet (RRP £16.99). To order a copy go to guardianbookshop.com or call 0330 333 6846. Free UK p&p over £15, online orders only. Phone orders min p&p of £1.99.