Shadow Country, By Peter Matthiessen

For some writers, their own works are, once finished, literally closed books. Like Virginia Woolf, they "shudder past them on the shelf as if they might bite". Not so for Peter Matthiessen, co-founder of The Paris Review, campaigner for the environment and indigenous peoples, and author of over 30 books. In Shadow Country, he has taken his three novels from the 1990s about the real-life American outlaw EJ Watson and reworked them into one giant, though as those novels had been culled from a single 1,500-page manuscript, what we have now must be close to its forbidding conception.

Shadow Country is not just an immense book, but an intense one. It requires slow reading, not because it is difficult in its language or its thinking, but because it has dug deep into the mulch of American history and can't dump its findings on us all in one go.

It works obliquely, and what it works on is the legend of Edgar Watson, a South Carolina-born farmer and sometime outlaw who settled in the Ten Thousand Islands off the Florida Everglades in the 1890s. He worked hard, and was respected and feared by his neighbours, but rumours of murders in his past clung to him, and more killings kept happening around him.

On one Monday morning in 1910 he was gunned down on the beach of Chokoloskee; 33 bullets were picked out of his body. Self-defence by honest men, or the work of a lynch mob? That is the question the book sets out to probe and, through that, the fiercer question of who EJ Watson was, and what he represented.

The story still comes split into three books. It begins with the shooting, and then opens the floor for first-hand accounts of Watson by those that knew him – an unstable mixture of "po' whites", "niggras" and "indins". Their testimonies shuttle to and fro along a timeline towards his death, building a rich but contradictory picture. Watson is "the friendliest son of a gun I ever met", "a fine farmer", "fallen angel", "red devil", "laughing killer".

Once he is safely dead, buried face down under two slabs of coral, the baton passes to his son Lucius – one of ten offspring, from three lawful and two common-law wives. Lucius's is the second book, as he attempts to cope with the death of his father, first by obsessively building a list of everyone present at Chokoloskee that October morning, and then, when he realises he doesn't have the stomach for revenge, researching a biography.

The narrative pushes back into Watson's past, and into the future, as the witnesses move on, their livelihoods threatened by the changing economy of the Everglades. If the first book was a thick mangrove swamp, this one is a slow-rolling river, happy to loop back towards its beginnings.

The third book is Watson's own, running right back to his childhood of "hard labor, lice, mean dirt, and poverty" during Reconstruction, and his abuse at the hands of a violent, drunken father. Watson's telling runs straight and true, showing how a wayward temper and a yearning for progress and advancement can derail even the best-intentioned of men.

If you can track back American literature to the twin sources of Moby-Dick and Huck Finn, then this book is truly of both their lineages. From Twain it takes its trust in the vernacular, its anti-racism and its certainty that freedom can be found within the confines of the USA, if not always its laws. From Melville it takes its tragic central character who will not, or cannot, settle for what is on offer, from God or man, but must reach for more.

There are echoes, too, of the Great American Novel That Dare Not Speak Its Name: the detective thriller, especially those, like Hammett's and Ellroy's, that trace crime back to corporate corruption – here, in the big sugar companies that want to burn off and poison the Everglades scrub. Shadow Country's size and scope may throw down a challenge, but anyone who takes it up will only be rewarded. If this isn't a great novel, American or otherwise, I don't know what is.