She was speaking too hastily, too bluntly, she knew that. It would seem shocking to a young man of family to imply that the head and back of a princess were much like anyone else's. But she was indifferent to his sense of propriety, such things were no longer important; and somewhere within her there was a sort of surprise at this indifference of hers, something she had never felt before, which had grown with the growing of her plan. 'No one will know it is not Iphigeneia,' she said. 'The victim will be wearing a mask.'

She told him then what she had told Odysseus earlier, the white clay, the moon-mask covering the features, so that the priestess of Artemis could walk with the goddess. 'They have agreed,' she said, 'they have given permission. Iphigeneia will make up my face with the paste. When they come for her, I will be the one with the white mask and the saffron robe. Iphigeneia will be dressed in the clothes of Sisipyla, the slave girl. When they are taking me out she will hide her face in grief. No one will pay any attention to her. When we begin the procession towards the altar, the people will be flocking to see me die, the camp will be deserted. The princess will make her way down here, to the shore, where you will have a boat waiting.'

'But afterwards, when your... when they wash the body to prepare it for burial, when the chalk is washed away, Agamemnon will know, he will see it is not his daughter.'

'A face so changed in death, after such loss of blood? How well does Agamemnon know his daughter's face? How much time has he spent with her in these recent years? Besides, even if so, what will he do?'

This too she had mulled over, lying on her back straight and still, hands by her sides for concentration, a habit of childhood, while the light slowly strengthened and the first songs of the birds sounded from the hillsides all round the camp. She said, 'Iphigeneia will be safe by then, you will be at her side, she will depend on you for support. And Agamemnon will be looking down at my dead face. The fleet is ready to sail, success awaits him, he has satisfied all the conditions.'

She paused, aware that her heart had quickened, aware of the need to breathe deeply. It was exhilaration she felt, not doubt or dismay; and still that same surprise at her indifference to everything but his agreement. Never had she spoken words so unhesitating, in such clear order. She was not the person she had been, at the altar she would die a different person. 'What will he do?' she said again. 'Will he declare to the army that there has been a mistake, that the wrong person has been sacrificed? He will keep the knowledge buried in his heart. And how can there be a wrong person, in any case? Surely it will be enough for Zeus that Agamemnon believed it was his daughter at the time of the killing. It is not a matter of bodies. My mistress and I are the same age, our bodies are the same. It is the belief of the King that matters.'

'That is true.' A light had come to Macris' face. 'It's the thought that counts,' he said. But the light had not come only from this comforting truth. He would be the princess's saviour and protector. He would stand alone with her against the world. She would be grateful to him. There were no rivals now. The day would come when Agamemnon too would be grateful for this substitution, grateful to the man who at a single stroke had confirmed him in his command and saved him from the shedding of a daughter's blood. And with the gratitude of kings there came very tangible benefits. 'Yes,' he said, 'yes, it could work. We could be across to the other side in no time. The current runs that way, I noticed it yesterday when we came off the ship. Yes, I will do my part, I will wait with the boat.'

He stood still a little while, looking down at her in silence. Perhaps it was her closeness to childhood that moved him at this moment – she was not yet full-grown. He reached out and laid a hand on her shoulder. 'You are made of good metal,' he said. 'The goddess will be with you, she will make things easier.'

On this she left him, returning alone. She was armed with two assurances now. Macris believed in the scheme, he would see to the boat; Odysseus had swallowed the idea of the moon-mask. She found Iphigeneia alone – Odysseus had just left, promising to return shortly.

'He gives me no rest,' the princess said. 'He tells me constantly that my death is certain, that I must turn it to account, that it must not be a death wasted.' She was dry-eyed now, and seemed composed, but the voice was toneless and she held her lower lip folded inward as if to keep the mouth firm. 'He says the deaths of great persons must not be wasted, their deaths must be in keeping with their greatness.'

'Odysseus is clever,' Sisipyla said. 'I felt it when he spoke to me. But he is wrong when he says the princess's death is certain.'

With this, in a voice not much louder than a whisper, taking great care to get everything in order, she began to outline the plan, whose marvellous simplicity had come to her, a shaft from Artemis, in the dawn of that morning. It was a better plan now for the double assurance contained in it. She had no way of knowing, as she spoke, how Iphigeneia was taking it, because the princess, after the first look of fixity, kept her face averted.

In the silence after she had finished, Iphigeneia turned to look at her and there was something in the princess's eyes that made her feel the prickle of tears in her own.

'You would do this for me?'

'Princess, you gave me my life, I am ready to give it back now if you will favour me and take it.'

Iphigeneia made a quick movement towards her and she found herself clasped in a close embrace. She felt a shuddering within the princess and this was transmitted to her own body and for these few moments their two bodies were a single vehicle for grief. Then Iphigeneia drew away and already her face had changed, there was a kind of sharpness in it. 'But how could you be mistaken for me?' she said.

'With the make-up, the moon paste...'

'Even masked, it would be seen that you were not the princess.'

'But Lady, how could it be seen?' It was the same objection that Macris had made. What would have been easy for her – recognizing that she could be confused with another – was hard for Iphigeneia, and this was something she had not fully taken into account. As if the princess bore a sign always about her, like a light round her head, or something like music, something everyone would recognize and know. With a firmness that came as a surprise to herself, she said, 'With the mask that makes the face round and white, with the robe of the victim, with the way I will walk, everyone will think it is Iphigeneia.'

It was the first time in her life that she had taken such a tone with her mistress, and she felt a kind of alarm at her temerity. But Iphigeneia showed no displeasure, merely compressed her lips and nodded once, as if considering.

'But are you sure you can go through with it? What if you lose your nerve halfway through?'

Sisipyla felt a flood of relief at this. Not a question at all really, only a doubt. It meant that the princess would agree. She had not thought for a moment that Iphigeneia would refuse the offer of a slave's life to save her own, fond as she knew her mistress to be of her; but she knew also that the princess had no high opinion of her powers of concentration, thinking her sloppy and unfocussed – she had said so often enough. She said, 'Once I step outside in the mask and the robe, once I take the first paces towards the altar, my death is certain. If they find out I am only Sisipyla, they will kill me. Why would I lose my nerve, knowing I am dead in any case?'

Iphigeneia was silent for a time that seemed long to Sisipyla. Then, in a tone in which there was no finality, only a sort of reflectiveness, she said, 'So I will prepare you for the sacrifice, dress your hair, spread the moon-mask on your face. You will be my substitute, you will honour the goddess in my name.'