She might look a while for men – there were few enough of them: there were families, and the scraps of families; widows and orphans. There were the remnants of men, who made up the army now. And every so often, it was true, there were men. They turned up. You saw them, squatting beside the morning fire, in their spurs and hat brims, the male contents of some village who had joined their quest – for it was hard to call it a war any more, or even a fight. And yet it was not nothing. It was the last battle, said Bernardino Caballero, a man who had seen enough last battles, you might think, to give him some inkling of when a war might end.

Or even, thought Stewart, of where the ending might have begun. At Angostura, perhaps, where the gallant Captain Thompson walked over to the enemy and handed up his sword. Or later, on the Azcurra heights, after yet another last battle: twenty thousand Brazilians against a battalion of women and children, with beards on their faces made of grass and wool; the new capital (a poor enough town) Peribibui lost. After that, Acosta Nu, held to the last minute by Caballero, so that Lopez might escape to San Estanislao – another 'capital city', this one lost without a bullet shot. Curuguati, then eastwards to the heights of Panadero. All of these places boldly marked on a map that Lopez had – though Stewart could point until his arm was sore at this far place or that, waiting for a Guarani to lend him its name.

After the carts and wagons came certain prisoners who were never shot. They comprised the life story of Francisco Lopez. Some woman he wanted. Some woman he did not want. A man who scorned him. The son of the sister of the man who betrayed them to the Brazilians at Curupaiti, or Curuzu. They were given more food than the common soldiers, so that they should not die when they were flogged. Some of them were quite hale, and Stewart wondered why they did not escape. Though how could they, when everyone here was escaping? They had been escaping so long, it made a man think that this was what life was – a regrouping against forces that are large – yes, admittedly very large – but also clumsy and beneath his contempt.

'Hah!' said Stewart, to illustrate his point, and the small girl who walked now with her hand always on his stirrup looked up at him and smiled.

She was a Guarani girl, of uncertain age.

They do not listen to words, Stewart noticed. These children only look, and it is always at the wrong place. They do not watch your eyes but your mouth. Or they do not watch your mouth but your hands. They make you feel not so much wrong-footed as wrong-faced. Or they might watch your eyes, but that is not the same thing as meeting them: a man might long for another human creature just to return his gaze. Perhaps that was what dogs were for. And he spent a while that day thinking about eyes – whether they were the door to the soul, or the soul's mirror. Do they open, or reflect, and what was the anatomy of it all.

He thought of the blue and stupid eyes of George Thompson at Angostura, looking at him while he fingered the hilt of his soon-to-be-surrendered sword. The table where they sat, with a sheet of ants lapping up and over the edge of it, on their way across the room. The rest of the ants walking happily on the floor.

Thompson's eyes of cerulean blue; a flare of white around the pupil, a matching outer ring of a darker smoky blue

– there was a pattern to this dark rim, as it fell towards the pupil, a kind of gothic veining. Which blue came first? Stewart was a doctor. He should know about such things, about the previousness, or lateness, of colour, and how colour grows. He should have paid more attention, at the time, to the bruised, navy colour of his own children's eyes, as they shifted into brown.

A British boat was waiting down river, Thompson said. It would take them to the Argentine, and then home. Stewart did not answer. He looked at the ruin of his hands, his cannibalised nails. He did not want to go.

And so his life was shaped by a kind of stickiness. He did not want to leave his family in Asuncion – those little strangers his wife had reared for him. He did not want to leave his wife – herself a stranger to the woman he had once loved. Besides, he could not abide Thompson. And so he drifted along with the war, which was not so much a stream as a sequence of separate moments, each so vivid and different from the last it made him feel quite hilarious, the way that nothing now was connected to anything else.

Thompson gave Stewart his horse that day. How did he surrender? Stewart sometimes idly thought. Did he walk?

The languorous dip and buck of the creature's back beneath him provoked thoughts of a slow, abrupt congress, but it was also conducive of other rhapsodies and regrets

– that he had not made a contribution, for example. There were trees around him demanding botany, and birds their taxonomy. There were things his aunt would have admired, if you set them on her mantel in a glass jar. There was the fame of exhibition: Ά series of glass eyes, blown and variously pigmented to the specifications of Dr Stewart, with a brief note of their metamorphosis and pathology. The eye of the diabetic patient, the eye of the bereaved woman, the eye of the blind.'

And there was a gorgeousness too, in not doing these things. In never having done anything, except go with the stream, which, although he cavilled, was not finally the stream of duty or obligation, but the flow of his own desire. The only time he went against his own inclination was when he stopped drinking: the rest – exile, marriage, the army, children – each an annoyance to him, and each the only thing he wanted to do at the time. He regretted the fact that he had lived a life of constant regret, and called an end to choice, with all its teasing grief. He looked instead at the life around him, from fungus to flower, and thought about eyes.

Sometimes he felt, as he rode, as though he were inside something; that he was looking out through the sockets of his eyes, as an antique soldier might look through a slit in his helmet. He felt that, between his skull and his self there was a gap, an area of darkness, across which he must peer.

At other times he felt that his eyes were as big as his face, and as open; his face itself was wide as the sky. But then the helmet was back again, and his eyes were darting through the gaps. Like bullets. He shot his gaze at a tree, at a bird. He never missed.

He wished he had a pen, or even that Venancia were here so he could share his observations with her. He was grown most chatty, and so he told the girl with her hand on his stirrup that the eye was not a door or a mirror, but a weapon, at war with the world. And she looked at him.

Some days later she surrendered. She met his eye, and then she did something with her own eyes. A kind of swoon, but without looking away. She made her eyes flat and unjudging, so they looked, he thought, quite gelid. Then – did they open? They became inviting, somehow, like water. The tiniest shift. A liquefaction. Just enough to say, 'Yes.' Or even, 'Please.'

Stewart's pleasure was not what it had once been. It was thin and weak and he did not know what to do with the body of this girl under him, which was very small. It seemed more like a bundle than a body, though hot inside – which struck him as sad. His desire was a meagre, hard blade with which he stabbed himself, not her, where once desire had been (he could hardly remember what it had been) – oceans, rivers, forests, God help us: everything. The girl was younger than he had thought and he did not take her again.

The last time Stewart slept with Venancia there was nothing to be done. Perhaps there had been some physical exchange, but he could not remember it as a carnal event. If, for example, he were to die, and in his dying try to remember the last time he had been inside his wife and the last time she had been about him, he would not be able to do so. As the journey went on, as the landscape unfolded in front of him and unravelled behind, he wondered if the people he had left in the past still existed. He wondered if there was any way to stitch the path back up, and make his way home to them. And he regretted the night he had lain in the dark at Venancia's side talking about warehouses, licences, a lawyer in Buenos Aires they both knew. They had a chance, and they did not take it. A chance for what, he was not sure. Desire was the least of it. But it was also, perhaps, a chance for desire.