The book opens with a sentence so famous in Spanish that children learn it the way English children learn the first line of Genesis. In a village of La Mancha, whose name I have no wish to recall. The refusal to name the place is already a joke: the narrator is pretending, with a straight face, that this story is too important to bother with geography, when in fact it is about a man for whom geography will dissolve entirely.

The hero is an aging country gentleman — fifty or so, lean, dried out, living on lentils and scraps with a housekeeper and a niece. His name is something like Quijada or Quesada; Cervantes cannot be bothered to settle it. What matters is that this man reads. He reads constantly. He reads chivalric romances — the fat, over-coloured novels about knights-errant and magicians and princesses that were the supermarket fiction of the late Renaissance. He sells pieces of farmland to buy more of them. He forgets to eat. He forgets to sleep. He argues with his neighbours about which knight was the greater. And one day, Cervantes tells us with a shrug, he simply loses his mind.

This is the greatest opening in European fiction, and everything else follows from it. Cervantes does not give us a mystic or a poet or a man in love. He gives us a reader. The first modern novel begins by diagnosing what reading can do to a person when there is nothing else in the life to push back. His madness is not alien to us; it is the logical extreme of our own behaviour when a book takes over.

And the diagnosis is tender, not contemptuous. Cervantes himself read the same books. He fought at Lepanto, lost the use of his left hand, spent five years enslaved in Algiers, and returned to Spain to be broke. If anyone had reason to think that chivalric fantasy was a lie, it was him. And yet the old knight he invents is treated with a care that reads, across four centuries, as something close to love.

The village does not want this to happen. The housekeeper and the niece will spend the next thousand pages trying to get him home. But the old man has decided. He takes down an ancestor's rusted armour, patches the helmet with cardboard, names his starved horse Rocinante, and goes out into the world to become the thing he has been reading about. The novel, and a new kind of person, begin together.

Before he can go anywhere he has to become someone. The gentleman of the nameless village chooses himself a new name — Don Quixote of La Mancha — because a knight without a proud toponym is not a knight. He chooses his horse a name — Rocinante, literally a nag that used to be a nag. And he chooses a lady, because no knight rides without one: a peasant girl from a neighbouring village whom he has seen perhaps three times in his life, renamed Dulcinea del Toboso. None of these people — the knight, the horse, the lady — are quite real. All three will outlast their century.

Then he rides out. The first night he reaches a roadside inn that he is determined to see as a castle. The innkeeper, who is a rascal but not an unkind one, plays along. He agrees to dub our hero a knight. He takes his ledger book — the one he uses to record what the muleteers owe him for wine — and reads from it as if it were a holy rite. He taps Quixote on the shoulder with a sword, charges him what he can, and sends him on his way.

What Cervantes discovers, in writing this, is the engine of the whole book. The world will keep being what it is. It will be inns, mules, dust, small-minded clergymen, scheming innkeepers' daughters. But Don Quixote will keep translating it. An inn becomes a castle; a flock of sheep becomes two armies; a barber's basin becomes the helmet of the Moorish king Mambrino. And because he translates with absolute conviction, the world starts, half reluctantly, to humour him. People play along. Sometimes out of kindness, sometimes for sport, sometimes because the fiction he is offering is more interesting than what their afternoon otherwise contained.

This is what makes him not just a madman but a force. Reality does not bend to him, exactly, but it visibly hesitates around him. The peasants he meets are changed by having met him, even when they pretend to be only amused. Something has entered their day that was not there before.

The first sally ends badly — he is beaten by some merchants on the road and carried home slung across a donkey. But the pattern is set. The novel will be the story of a man who cannot stop believing in an impossible vocation and a world that cannot quite decide whether to laugh at him or follow him.

The first sally had a horse but no squire, and that was the problem. A knight-errant needs a foil — a down-to-earth companion to whom the world can be explained, to whom errors can be pointed out, and in whose company the road itself becomes a conversation. So before the second sally Don Quixote recruits a neighbour: Sancho Panza, a married peasant with several children, a belly, and a donkey.

Sancho is poor and Sancho is worldly. He joins Don Quixote on the explicit promise that his master will, someday soon, conquer an island and hand him the governorship. This promise is ridiculous. Sancho knows it is ridiculous. He also knows that his life without the promise is shovelling pig feed. So he saddles his donkey and goes.

He is the single greatest invention in the novel, and it is possible Cervantes did not realise he was inventing him. Sancho begins as a stock device — the stupid peasant — and within a hundred pages has become something else. He loves his donkey. He quotes proverbs at triple the rate of the language's normal intake, in one chapter stringing together so many that his master has to beg him to stop. He gets hungry and says so. He cries when his donkey is stolen and laughs until he wets himself when the strange ways of the world are pointed out to him.

And slowly, over the hundreds of pages and mile-long conversations on the road, Sancho learns his master. He does not catch his madness. He keeps insisting that the giants are windmills, that the army is a flock of sheep, that the Moorish king's golden helmet is just a barber's basin turned upside down on a bald head. And yet something in the conviction of the knight works on him. By Part Two, when Sancho is asked by a cynical duke and duchess to govern a pretend island as a joke, he turns out to be a wise and fair-minded governor. He listens carefully. He settles disputes with proverbs and peasant common sense. He resigns before they can humiliate him more.

This is what Cervantes does with the two of them. The knight lends the squire gravity; the squire lends the knight humanity. Alone, each would be a cartoon. Together they are a marriage. The novel spends its length showing what that marriage teaches each of them — the madman who slowly, very slowly, comes to see; the peasant who, never abandoning the donkey or the proverbs, quietly becomes a gentleman.

It is the scene everybody knows, usually badly. Don Quixote and Sancho come out onto the open plain and see thirty or forty windmills turning in the wind. The knight, visibly excited, tells his squire that fortune has given them a gift: behold, there stand thirty or more lawless giants, whom he intends to slay in fair combat. Sancho, squinting, points out that they are not giants but windmills, and that what he is calling arms are the sails. Quixote answers that Sancho knows nothing about adventure: these are giants, and if he is afraid he should go and say his prayers while a real knight engages them.

He couches his lance and charges. He spears the sail of the nearest mill. The wind, turning the mill, lifts him horse and all and breaks the lance to splinters, then drops him hard into the field. Sancho rides up on his donkey. Are you all right. Quixote, having the wind knocked out of him but not the story, explains that a wicked enchanter — the same one, no doubt, who has been persecuting him for chapters — has transformed the giants into windmills at the last moment, purely to rob him of the glory of the victory. He mounts up, sore, and rides on.

Four centuries later, tilting at windmills has become a shorthand for fighting an imaginary enemy, for wasting your energy on a battle that does not exist. Cervantes does not exactly disagree. But he also complicates the phrase. Because look at what the scene does. Ninety-nine readers in a hundred remember that Don Quixote attacked windmills thinking they were giants. They do not remember that at the end of the paragraph he explains away his defeat by blaming a wizard.

That second move is the one that matters. It is not the first misperception that defines Quixote — anyone can mistake a mill for a giant in the right light — it is the refusal to update. No incoming data will be allowed to dislodge the frame. The enchanter did it. The enchanter is always doing it. The book will do this twenty more times. A barber's basin will turn into the helmet of Mambrino and, when challenged, into a basin-helmet. A flock of sheep will become two armies and, when shepherds start pelting him with stones, will go on being armies.

Which turns the windmill joke inward. We have all done this. We have all, under a strong conviction, pressed on through contrary evidence by inventing a persecuting enchanter — ideological, romantic, professional. Quixote is not special. He is only more committed. The scene is funny the first time, and then it is funny and dreadful on the second reading, and then on the third it is simply you.

Every chivalric knight owes a lady, and so Don Quixote, in his first fit of preparation, selects one. A peasant girl named Aldonza Lorenzo, from the nearby village of El Toboso. He has, by his own admission, spoken to her perhaps three times. She is by all accounts a stout farm woman with powerful hands who can salt pork faster than any woman in the district. He renames her Dulcinea del Toboso, sends his sighs in her direction, and vows to her every deed of arms he undertakes.

She never appears. She never receives a message. She does not know she is the lady of a knight. In Part One, Quixote is seized once with the idea of retreating to a hermitage in the Sierra Morena to do mad penance for her — for a wrong she has not done, which he has not been told about, and about which he has no evidence — in the manner of Amadís of Gaul. He tears up his shirt, hangs it on a bush, and lies down naked to lament. Sancho watches this, appalled and weeping, and is at last dispatched with a love letter to deliver personally to her door.

Of course Sancho cannot deliver it. He loses the letter. He lies. He tells Quixote he delivered it and that she was winnowing wheat in her yard and received the news with grace. Quixote is delighted. He does not require the wheat or the winnowing to be real; he only requires the image, which Sancho has obligingly supplied.

In Part Two — published ten years after Part One — the issue becomes sharper. A reader, now, might ask the question that never occurred to Part One. If Dulcinea does not exist, what kind of love is this. Cervantes lets Sancho carry the crisis. Outside El Toboso one evening, the two of them see three peasant women on donkeys coming out of the village — real, present, snub-nosed, hard-faced women. Sancho, who has been caught out and needs to improvise, tells his master that these are Dulcinea and her ladies-in-waiting. Quixote looks and sees exactly what is there: three peasant women on donkeys. He does not see a princess. He is horrified. The enchanter, he concludes, must have transformed the real Dulcinea into this rough form to rob him of the sight of her true face.

It is one of the strangest moments in the book, and it is why Dulcinea is not a joke. The man who has been translating the world into chivalric fantasy for a thousand pages here refuses, when the fantasy is handed to him, to translate at all. He knows the real peasant women are not his lady. And he grieves for the missing version like a widower. Cervantes is showing us what love at a distance actually is: it is accurate about the beloved and wrong about the world, and it will, in the end, be the sadness that kills the old knight.

On a dusty road one afternoon, master and squire meet a chain gang: a line of twelve convicted criminals being led to the coast to row the king's galleys. Chained at the neck, guarded by officers with crossbows and arquebuses. Quixote, never one to pass up an injustice, rides up to interview them. He asks each man why he is in chains. One stole a washbasket. One cheated at cards. One was a pimp. One is the famous thief Ginés de Pasamonte, who proudly announces he is writing the story of his own life — a book, he says, that will be so good that all other rogue autobiographies will have to shut up shop.

Quixote listens to the whole line. He is moved, because what he has been told by his books is that the king's mercy ought to fall on the unfortunate, and because — cutting through the grandness — he is a man who has just spent half an hour listening to twelve other men tell him about their lives. He announces that in the name of heaven he cannot permit free men to be led in chains against their will. The guards explain that these are not free men; these are sentenced criminals of the Crown. Quixote explains that he does not recognize that distinction. A small, very one-sided fight ensues. Quixote fights hard; Sancho, appalled, watches. The guards are driven off. The prisoners are freed.

And here Cervantes performs the move that separates him from every other comic novelist of the sixteenth century. He does not let Quixote be rewarded. The freed prisoners, with Ginés leading them, now a thoroughly armed band with nothing to lose, listen politely to their deliverer's next request — that they proceed together to El Toboso and pay their respects to the lady Dulcinea. They decline. They in fact strip Quixote and Sancho of most of their belongings, stone them, and run. The knight, liberated, is left beaten and robbed on the road by the men he has just liberated.

This is the darkest joke in the novel, and also its warmest. The freed men behave as freed men do: they look after themselves. They do not feel gratitude at the level the books had promised. And yet Cervantes is not telling us the liberation was wrong. He is telling us, simultaneously, that the old gentleman on the bony horse did a genuinely good thing — one of the few genuinely good things anyone does in the entire Spanish Golden Age around him — and that good deeds of this size do not produce storybook outcomes.

The beating is serious. Quixote gets up anyway. It is impossible to watch and not to love him a little more.

He goes home to die. After a last sally, a last beating, a last long ride across the dusty plain with Sancho, the old knight falls ill and takes to his bed. His niece is there. His housekeeper. The village priest. The local barber. And — the most important part — Sancho. He has had a fever and he is weak and he has slept a long time. And when he wakes, his mind is clear in a way it has not been clear since the book began.

He calls for the priest. He speaks quietly. He says: I am no longer Don Quixote of La Mancha. I was never really him. I am Alonso Quijano, whom my neighbours, for my mild ways, once called the Good. He renounces, carefully and without flamboyance, the chivalric books and everything he has done under their influence. He confesses. He makes a will. He forgives.

Sancho does not take this well. Sancho, who through a thousand pages has begged his master to be sensible, now kneels at the bedside and weeps and begs him, one last time, to be mad. Do not die, sir. Get up. We will ride out again as shepherds, you and I, and live in the fields, and you can be a great shepherd, Don Quixotiz, and I will be Panzino, and we will find Dulcinea under some tree turned into a beautiful sheep. The squire is saying, in effect: please stay inside the book with me. The knight looks at him with the kindness he has always looked at him with, and tells him gently that there are no birds left in this year's nests. Then he dies.

It is an astonishing ending. After two thousand pages of joke and adventure and windmill and braying donkey and cardboard helmet, Cervantes permits the hero a few pages of perfectly calm sanity and lets him die in them. We have been laughing at the old man for a book and a half, and suddenly we are standing at his deathbed and he is the most serious person in the room and we do not want him to go.

The book ends with a notary's formal note that Don Quixote is dead and that nobody is to resurrect him — a specific jab at a spurious sequel someone had published in the meantime. But the last real sentence belongs to Sancho. The squire walks out of the room with the others. He says nothing for a while. He goes to look at his donkey.

The first modern novel turns out to be about the difficulty of leaving a book, and the necessity of doing so. Alonso Quijano, by dying sane, gives his reader permission to close the volume and go on with a real life. And then, immediately, the reader misses him.