She was, in the first instance, more beautiful. Stewart was at the age when men become addicted to youth, so Eliza's increasing, and increasingly new, beauty was a mystery to him. She was, by general standards, old. She was also fussy. She came into his medical tents with a great show of entourage and ladies, and you might think the men would find it an irritation, but the truth was that her face was a solace to them, her smile a balm, and the few words she uttered (to Stewart's sometime annoyance) a cure in themselves. And it was not just the gullible and the forgotten who felt the force of it. When she entered a room – it might be some bare room in the camp at Léon – when the men scraped their chairs back and stood, it was more than courtesy that moved them, it was the knowledge that, unlike the wives-daughters-sisters-camp girls, she understood the gravity of their great enterprise, and that, in some lovely, easy way, she belonged to them all. The most beautiful woman in the world.

So this was the first thing that Stewart had to tell Eliza, in the incongruous dark, by the side of the road – that she was beautiful. The second thing he had to tell her was that she was evil, too.

It was not a word he might casually use, but the war was exciting as religion to him now, and it was vital to keep Lopez pure. II Mariscal slapped his crop against his boots, he stalked, he was everywhere; and when the band played ' La Palomita', he looked twice as large and very fine. And in his stalking, slapping way, he might have a man whipped, or a man shot. He might have late dinners, which a woman would be wise not to attend. This is what Stewart wanted to say: that Eliza must strike with her Great Friend an attitude – such a one as you would find, indeed, on an old vase. She might fall on her knees. She might soothe. She might plead. But she must stay away from early whippings and late dinners. And she must never, ever whisper in his ear.

As he had seen her do, quite recently, as they stood on the dais at Cerro Léon. It was during a grand parade. She whispered, he laughed; then they both turned back to watch as men marched past on their way to the grave. Eliza's face, without changing at all, had become implacable, somehow, or greedy. Or hideously serene. She had gone from Angel of Mercy to Angel of Death, without a blink of her lovely eye.

Was it too late to turn back? Was there any other way for her to go? Stewart wished that Lopez would marry her – he almost longed for it. He felt, in the most foolish part of himself, that there might be something this woman could do – a bedroom something that their beautiful Eliza might say to their impetuous Mariscal that would stop it all, the torment and horror that was about to descend on them. Because it was the fate of angels, was it not, to intercede?

And now here she was, her ordinary flesh beside him on the roadside, and Stewart her protector. She was smiling at him, after pulling at his arm and letting it drop. He had just said her name.

'Eliza.'

'Yes?' she said, and took his elbow again, quite patient and sisterly.

'Be careful,' he said. And this time he walked on with her, because, pathetically, he did not know what else to say.

Ί am always careful,' she said (evil, quite evil) and the toes of her satin shoes slipped, one after the other, out from under her dress and on to the grit of the road.

It was not far to her house. She talked, remarkably, of Southern England, the small town in Kent where she had been married. 'For I am married, you know', to a M. Xavier Quatrefages. A beast, but a very minor beast, she said. A horse doctor in the military. But Kent was beautiful, all the same. The Weald – was that Kent? Perhaps it was Surrey. And so they came to the gate of her quinta, where she turned and took his hand in hers, and he, like some village Romeo, pushed forward to kiss her on the mouth. Or on the cheek. Or he brushed his mouth against the skin of her face, as she turned away.

He did not even like the woman. It was a part he was obliged to play, and she, to complete the scene, turned and fled prettily into the house. The theatre of it annoyed him, but not as much as the riot in his blood that had been gathering ever since he tracked her in the dark. He felt trifled with. He felt tempted, and scorned. Even if this were true (and it was not true) – no matter. What mattered was the violence with which he had wanted her, a woman talking of Kent or was it Surrey, as though she did not want him too. Was this passion? This epilepsy?This urge to destroy, like a child in a fit, the room, the house, the entire world? And that anatomical thing, his member, foolishly forward, seeking a place he could no longer imagine, let alone name, until there, on his hand, an appalling, imagined wetness; poor forked animal that she was. Gone now, through the gates of her house. Gone to bed.

He shook it off like a dog and headed back to town, and like a dog, he felt he had been whipped. But the road was straight and he knew where he was going. He was going to his annoying wife Venancia for some love. Just that. The odorous cushion of her breast beneath his ear.

For a long time, the memory of that night's encounter clung to Stewart like a dream you cannot wash off in the morning. It returned, in one detail or another – the sound of the insects in the dark; the turn in the road; and what might have happened if some different move had been made. If he had spoken more, or better. If he had stopped. If one or other thing had shifted even slightly and he had ravished, or been ravished by, a woman he did not even like, who walked out at night as he did, alone.

Nothing much, of course. The sexual act. A different way of looking at Lopez. His own throat quietly slit perhaps (or perhaps not). A great passion, or no great passion. A mess. Any number of things, none of which would increase the sum of his pleasure in seeing Eliza secretly in the dark, as though she had invited him to this assignation, and him alone.

Of course she was not there for him. What Stewart knew – but did not realise for some time – was that Eliza's stillborn daughter was buried in the graveyard along whose walls she walked that night. It came to him, seven years later, when he buried a child for Venancia, who could not attend, being not yet churched. It was their sixth, a meagre little daughter who died as soon as she was born. They scraped out some earth and put her in. Stewart looked up, and Venancia's absence on the other side of the tiny grave made him think of other ghosts – the lilac paleness of Eliza that night, in the June of 1865, when the war was still something you might win or lose.

The graveyard was beautiful. It was one of those blessed days when you thought there could be no hardship in such a place and with such weather. The jacaranda trees were in smoky bloom, the birds sang into the stillness, and the whole world seemed to whisper 'Afterwards. Afterwards'. It was all finished, now. The war. Lopez. Any number of dead. Stewart found it hard to care, after so much slaughter, for his own tiny child, but of course he did care, and the animal sorrow he felt seemed so unfair – that you should never be free of it, that, like hunger, pain would always be new and hard. And as he turned away he remembered that Eliza's daughter was buried here too. So that was what brought her out along the road that last night in Asuncion. She had come to visit the bones of her baby – so light and tentative and barely formed. He thought of them as they lay in the earth now, open and loose; melted back from each other where the cartilage had not had a chance to harden into bone.

Stewart stepped back with a snort that surprised the gravedigger. He had remembered – but last of all – the kiss. And with the memory came the thought that the kiss, despite its opiate clarity, might not have been a kiss, after all. Also, and either way, that it did not matter now. Perhaps it had not mattered then. And Stewart felt a fierce nostalgia for the war. Standing alive, as he stood now, among the great sighing mass of the dead.