Strangely, it was Tolui who saw his uncle's distress and he spoke kindly. 'I think I will be better on my own for the moment, uncle. I have my son as a comfort to me. He will take my messages home. I will need you later on, at sunset.' He sighed. 'I will need you to stand by me then, without a doubt. Now though, I still have words to write and orders to give.'

'Very well, Tolui. I will come back as the sun sets. I tell you one thing: when this is over, I am going to kill that shaman.'

Tolui chuckled. 'I would expect nothing else, uncle. I will need a servant in the next world. He would do very well.'

The young slave returned bearing an armful of clean, woollen clothes. Bare-chested, Tolui pulled rough leggings up his thighs, concealing his manhood from view. The slave tied the thong at his waist while Tolui stood with his arms out, staring into the distance. His women had begun to weep and neither man rebuked them for it. Tolui was pleased to hear the crying of women for him. He dared not think of Sorhatani and how she would react. He watched as Khasar mounted his horse once more, the older man silent with misery as he held up his right hand and turned to ride away.

Tolui sat on the grass and the slaves knelt before him. The boots were new, soft leather. The women bound his feet in untreated wool and then pulled the boots over them, tying them with quick, neat movements. Finally, he rose.

The deel robe was the simplest he owned, a lightly padded cloth with almost no decoration beyond buttons shaped like tiny bells. It was an old piece that had once belonged to Genghis and it was marked with the stitching of the Wolf tribe. Tolui ran his hands over the coarse design and found he could take comfort from it. His father had worn it and perhaps there was a hint of his old strength left in the cloth.

'Walk with me for a time, Mongke,' he called to his son. 'There are things I want you to remember for me.' The sun dipped on the last day, spreading a cool light that slowly lost its colours, so that the plains softened into grey. Sitting cross-legged on the grass, Tolui watched the sun touch the hills in the west. It had been a good day. He had spent some of it rutting with his slaves, losing himself for a time in the pleasures of the flesh. He had appointed his second in command to lead the tuman. Lakota was a good man and loyal. He would not shame Tolui's memory, and in time, when Mongke had more experience, he would step aside for the son.

Ogedai had come to him in the afternoon, saying that he would appoint Sorhatani the head of Tolui's family, with all the rights her husband had known. She would retain his wealth and the authority over his sons. On his return home, Mongke would be given Tolui's other wives and slaves as his own, protecting them from those who would take advantage. The khan's shadow would keep his family safe. It was the least Ogedai could offer, but Tolui felt lighter after hearing it, less afraid. He only wished he could speak to Sorhatani and his other sons one last time. Dictating letters to his scribes was not the same and he wished that he could hold his wife, just once, that he could crush her to him and breathe in the scent of her hair.

He sighed to himself. It was hard to find peace as the sun went down. He tried to hold on to every moment, but his mind betrayed him, drifting and coming back to clarity with a start. Time slipped like oil through his hands and he could not hold a single instant of it.

The tumans had gathered in ranks to witness his offering. Ahead of him on the grass, Ogedai stood with Khasar and Mohrol. Mongke waited slightly apart from the other three. Only he looked directly at his father, a constant gaze that was the sole sign of the horror and disbelief that he felt.

Tolui took a deep breath, enjoying the scent of horses and sheep on the evening breeze. He was pleased he had chosen the simple garb of a herdsman. Armour would have choked him, confined him in iron. Instead, he felt loose-limbed, clean and calm.

He walked towards the small group of men. Mongke stared at him like a stunned calf. Tolui reached out and drew his son into a brief embrace, releasing him before the shuddering he felt against his chest turned into sobs.

'I am ready,' he said.

Ogedai lowered himself to sit cross-legged on one side of him, Khasar on the other. Mongke hesitated, before sitting to one side.

There was a certain shared animosity as they all watched Mohrol set a taper to brass pots. Thin trails of smoke dragged their way across the plain and the shaman began to sing.

Mohrol was bare-chested, his skin marked in stripes of red and dark blue. His eyes looked out from a mask that seemed barely human. The four men faced west, and as the shaman worked his way through six verses of the song of death, they stared at the setting sun, slowly eaten by the horizon until there was just a fat line of gold.

Mohrol stamped the ground as he finished his verse to the earth mother. He jabbed a knife into the air as he called on the sky father. His voice grew in strength, a double tone from his nose and throat that was one of the earliest sounds Tolui could remember. He listened distractedly, unable to look away from the golden thread that bound him to life.

As the verses to the four winds ended, Mohrol passed a knife into Tolui's cupped hands. Tolui stared at the blue-black blade in the last light. He found the calm he needed. Everything around him was sharp and defined and he breathed deeply as he pressed the blade against his skin.

Ogedai reached out and clasped his left shoulder. Khasar did the same with his right. Tolui felt their strength, their grief, and it steadied the last of his fear.

He looked at Mongke and saw the young man's eyes were brimming with tears. There was no shame in it.

'Look after your mother, boy,' Tolui said, then looked down and took a deep breath. 'It is time,' he said. 'I am a fitting sacrifice for the khan. I am tall and strong and young. I will take the place of my brother.'

The sun vanished in the west and Tolui pushed the knife into his chest, finding the heart. All the air in his lungs came out in a long, rasping breath. He found he could not breathe in and struggled to control his panic. He knew the cuts that had to be made. Mohrol had explained every detail of the ritual. His son was watching and he had to have the strength.

Tolui's body had gone tight and hard, every muscle straining as he sipped air back in and wrenched the blade between his ribs, cutting his heart. The pain was a burning brand in him, but he pulled out the knife and looked in astonishment at the rush of blood that came with it. His strength was fading, and as he began to fall forward Khasar reached out and took his hand in fingers that were impossibly strong. Tolui turned his eyes to him in gratitude, unable to speak. Khasar guided his hand higher, holding the grip closed so he could not drop the blade.

Tolui sagged as Khasar helped him draw the edge across his neck. He was frozen, a man of ice, as his warm blood drained into the grass. He did not see the shaman hold a bowl to his throat. His head lolled forward and Khasar gripped him by the back of the neck. Tolui could feel the warm touch as he died.

Mohrol offered the brimming bowl to Ogedai. The khan knelt with his head down, staring into darkness. He did not let go of Tolui's body, so that it remained upright, held between the two men.

'You must drink, my lord, while I finish,' Mohrol said.

Ogedai heard and took the bowl in his left hand, tipping it back. He choked on the warm blood of his brother and some of it dribbled down his chin and neck. Mohrol said nothing as the khan steeled himself and fought the urge to vomit. When it was empty, Ogedai tossed the bowl away into the gloom. Mohrol began to sing the six verses once again from the beginning, drawing the spirits close to witness the sacrifice.