As the scouts dismounted, Tsubodai waved a hand in their direction.

‘I know,’ he said. ‘Go and tell the other generals. We will hit them here.’

In the distance, he saw the shah’s outriders cutting dusty lines through scrub crops as they rode north. Tsubodai tried to put himself in the shah’s position, but it was hard. He would never have brought such an army through a single pass. Instead, he would have gone round the mountains entirely and let Otrar fall. The distances would have delayed the shah for another month in the field, but the Mongol tumans would have been forced to meet him on open ground, with all advantages stolen away.

Instead, the shah took the easiest route, showing that he valued Otrar. Tsubodai was learning everything he could, noting every decision that would help to destroy his enemy. He knew as well as anyone that Genghis was over-extended in this realm. It was no longer a matter of bringing vengeance to one city, but simple survival for their people. They had stuck their hands into a wasps’ nest every bit as furious as the Chin empire and once again the stakes were at their highest.

Tsubodai smiled at the thought. Some of the men fought for new land, for exotic women, even for gold. From his private conversations with the khan, Tsubodai knew he and Genghis cared for none of those things. The sky father gave a man his life and nothing else. The khan’s people were alone on the plains and it was a savage loneliness. Yet they could ride and conquer, take cities and empires one by one. Perhaps in time those who followed them would be as weak and soft as the city-dwellers they faced, but that did not matter to Tsubodai. He was not responsible for the choices of his sons and grandsons, only for the way he lived his own life. As he knelt on hard grey stone and watched the clouds of dust come closer below, he thought again that he had only one rule, which guided everything he did.

‘Fight for every breath and step,’ he muttered aloud, the words a talisman to him. It was possible that the shah’s great army could not be stopped, that it would roll over the tumans of Genghis, right to the plains of home. Only the sky father knew. Like the khan, Tsubodai would still seek out anyone who might ever be a threat and hit them first and harder than they would believe. With that, when he came to the end of his life, he would be able to look back with pride and not shame.

Tsubodai broke off his thoughts as riders from Kachiun and Jelme cantered up to his position. After days in that place, he knew them all by name and greeted them. They dismounted and bowed deeply, honoured by a general who remembered such details.

‘The tumans are coming, general,’ one of them said.

‘Do you have orders for me?’ Tsubodai replied.

The scout shook his head and Tsubodai frowned. He did not enjoy being set under Kachiun’s command, though he had found him a solid leader.

‘Tell your officers that we cannot wait here. The shah could still send men around us. We need to sting him, to force him along the route we have chosen.’

Tsubodai looked up with the others as Kachiun and Jelme came riding in, leaping down from their horses and striding to the high crag. Tsubodai rose and dipped his head to Kachiun.

‘I wanted to see for myself,’ Kachiun said, staring out onto the farmland below. The shah’s army was only a few miles away and they could all see the front ranks through the dust. It came on as a solid block and the sheer size of it was enough to alarm any man.

‘I have waited for your orders before moving, Kachiun,’ Tsubodai said.

Kachiun glanced sharply at him. He had known the young general when he was just another warrior, but Genghis had seen something valuable in him. He reminded himself that Tsubodai had repaid his brother’s trust many times.

‘Tell me what you have in mind,’ Kachiun said.

Tsubodai nodded.

‘This is a huge army, ruled by one man. The fact that he has chosen to come through this pass shows that he does not have our structure of officers. Why did he not trust two good men to take columns through the other passes? Know the enemy and you will know how to kill him. It is all useful to us.’

Kachiun and Jelme looked at each other. As experienced as they were, Tsubodai had a reputation for keeping his warriors alive that was unmatched in the tribes. He spoke without haste and all the time the shah’s army was drawing closer.

Tsubodai saw Jelme glance over his shoulder and smiled.

‘We hit them with that weakness,’ he continued. ‘We have thirty minghaans between us, each commanded by a man who can think and act on his own. Our strength is in that and in our speed.’ He thought again of wasps as he went on. ‘We send all but four out against them. Like a swarm. Let the shah try and crush them with his clumsy hands. We are too fast for them.’

‘And the four thousand men who stay behind?’ Kachiun asked.

‘The best archers,’ Tsubodai replied. ‘The very best we have. They will line the pass, high in the rocks. You showed the power of our bows at the Badger’s Mouth pass, did you not? I cannot find a better example.’

Kachiun twisted his mouth at the praise. Against Chin cavalry, he had once stood with nine thousand men and hammered shafts at them until they had broken.

‘If I keep the men low enough on the rocks to be accurate,’ he replied, ‘the shah’s archers will pluck them down with their own shafts. We don’t even know how those elephants will act in war.’

Tsubodai nodded, unconcerned.

‘No plan is perfect, general. You must use your judgement to place your men, of course, though they will have more range shooting down than up, no? I have said how I would tackle this shah and his host. Even so, I will follow your orders.’

Kachiun thought only for a moment.

‘Pray you are right, Tsubodai. I will send the men out.’

Tsubodai chuckled, surprising both Jelme and Kachiun.

‘I do not pray to anyone, general. I think if I did, the sky father would say, “Tsubodai, you have been given the best fighting men in the world, generals who listen to your plans and a foolish, slow moving enemy, yet you are still looking for an edge?”’ He chuckled again at the idea. ‘No, I will use what we have. We will take them apart.’

Kachiun and Jelme looked once more at the immense enemy marching towards the pass. A hundred and sixty thousand men were coming with their blood up, but somehow they seemed less terrible after Tsubodai’s words.

Shah Ala-ud-Din Mohammed jerked as his army let out a great shout all around him. He had been playing chess with himself to pass the hours and the set slipped from the small table in the howdah, scattering pieces. He swore under his breath as he yanked back the curtains at the front, squinting into the distance. His eyes were not strong and he could only make out bodies of horsemen coming at his army. Alarm horns sounded across the host and Ala-ud-Din felt a spasm of fear as he turned to look for his servant. Abbas was already running alongside and leapt nimbly to the wooden mounting step. Both men stared across two miles to where the Mongols rode.

‘Will you say nothing, Abbas?’

The servant swallowed nervously.

‘It is… strange, master. As soon as they are out of the pass, they sheer off and take different directions. There is no order to it.’

‘How many?’ the shah demanded, losing his patience.

Abbas counted quickly, his mouth moving with the strain.

‘Perhaps twenty thousand, master, but they move constantly. I cannot be certain.’

Ala-ud-Din relaxed. The Mongol khan must have been desperate to send so few against him. He could see them better now as they galloped towards his marching army. They rode in strange patterns, weaving and overlapping the groups so that he could not see where they would strike first. No orders had yet been given and his men marched stoically on towards the pass, readying their shields and swords. He wished Khalifa’s riders were there, but that was merely revisiting empty anger.