Genghis dismounted, showing his temper only when a raven came swinging in too close to him and he batted furiously at it, sending the bird tumbling in the air. Many of the carrion crows were almost too full to fly and merely hopped from body to body, opening their black wings and beaks as if in warning.

Genghis did not look at the corpses, except to estimate their numbers. What he saw did not please him. He stood over the two scouts and felt his patience fray in the heat.

‘Get up and report,’ he snapped.

They leapt to their feet, standing as if at an execution. No one knew how Genghis would react to a defeat.

‘General Kachiun has followed the enemy into the mountains, lord. He said he will leave other men behind to bring you to him.’

‘You are still in contact?’ Genghis asked.

Both men nodded. It used valuable warriors, but the practice of establishing a line from one site to another was nothing new. Barely five miles lay between scouts and they could pass information for twenty times that distance in just a short time.

‘There were false trails, lord, but the tumans are searching every valley,’ a scout said. ‘I have no news of a true sighting, not yet.’

Genghis swore and both scouts tightened their faces in fear.

‘How do you lose sixty thousand men?’ he demanded.

Neither scout was certain if the question required an answer and they looked at each other in desperation. Their relief was obvious when Jebe rode up to join Genghis, looking around him at the battlefield with an experienced eye. As well as the slabs of stone placed to break a charge, he could see trenches, some with dead warriors and horses still in them. Wooden stakes bound together had been broken or knocked to one side, but the rusty stains of blood could still be seen on some. There were hundreds of bodies in Arab robes, lying in pitiful heaps as birds and other animals tugged at their flesh. It was not enough, not nearly enough, and Genghis could hardly control his indignation. Only the thought that he must not criticise his generals aloud held his tongue. He knew Jebe could see the truth, but with Ogedai and Tolui within earshot, Genghis remained silent. Jelaudin’s army had fortified a position, just as a city or town. Kachiun had tried to break the defences by force, instead of standing back and waiting for them to starve. Genghis glanced at the sun beating on the back of his neck. Thirst would have killed them first, no matter how well they had prepared. To attack such a position was reckless, though he supposed he might have done the same. Still, his brother’s wits had deserted him. Genghis grimaced as he turned to Jebe, seeing the same thoughts reflected in that dark face.

‘Discuss the weaknesses of the strategy with my sons when we make camp, general,’ he said. ‘This prince should have been stopped here. Now we have to hunt him.’

He turned back to the scouts, who still stood, swallowing nervously.

‘There is nothing else to see here, nothing that pleases me. Show me the way to my brother and the next scout in the chain.’

Both men bowed and Genghis rode with them, his tumans coming after him in perfect order as they crossed the valley of Panjshir and entered a narrow crack, almost invisible in the brown rocks. It was barely wide enough for the horses to go through.

It took eight more days before Genghis reached Kachiun’s tumans. In that time, he had not allowed his men to stop long enough to cook food, even if they had been able to find wood for a fire. The mountains in that region seemed bare of life, populated only by lizards and high nests of birds. When warriors came across a stunted tree, they chopped it down with axes and tied the wood to spare horses to be used later.

As he went, Genghis rolled up the line of scouts Kachiun had left behind, bringing each man with him as the tumans travelled deeper into the maze of canyons and valleys. At times, they rode their mounts over slopes of rock almost too steep to remain in the saddle. There were no tracks left there. Genghis and Jebe began to appreciate the difficulty of the task for Kachiun. It was hard even to know which direction they faced, especially at night, but the line of scouts knew the way and they made quick progress. When they came upon the rear of Kachiun’s tumans, Genghis took Jebe and his sons through to the front, looking for Kachiun. He found him on the morning of the eighth day, at a brackish lake surrounded by towering peaks.

Genghis made a point of embracing Kachiun, letting the men see that he held no grudge for their defeat.

‘Are you close?’ he said, without preamble.

Kachiun saw the banked anger in his brother and winced. He knew better than to explain himself, having no doubt at all that Genghis would discuss his errors in great detail when they were alone.

‘Three false trails headed east, brother, but the main force is going south, I am certain of it.’ Kachiun showed Genghis a piece of horse dung, teasing it apart in his hands. ‘Still moist, even in this heat. We cannot be more than a day behind them.’

‘Yet we have stopped,’ Genghis said, raising his eyebrows.

‘I am running low on water, brother. This lake is salt and useless to us. Now you are here, we can share skins and move faster.’

Genghis gave the order immediately, without pausing to see the first waterskins brought up. He had thousands on his spare horses and the animals were used to sucking at them as if they had never forgotten their mother’s teats. He felt every delay as a spur to his growing irritation. It was hard not to berate Kachiun with so many watching the exchange. When Khasar and Jelme came to greet him, Genghis could barely look at them.

‘Tsubodai has orders to join us when he returns,’ he said to the three generals. ‘What is past is past. Ride with me now and redeem yourselves.’

A flicker of movement caught his eye and Genghis squinted up against the sun. On a peak, he saw a distant man waving a banner above his head. He looked back at Kachiun, incredulous.

‘What is that?’

‘The enemy,’ Kachiun said grimly. ‘They have watchers on us all the time.’

‘Send six good climbers up and kill him,’ Genghis said, forcing himself to remain calm.

‘They choose places one man can defend. We move past them too quickly to waste time getting them down.’

‘Has the sun softened your head, brother?’ Genghis demanded. Once more he had to struggle to control his temper. ‘Those are Jelaudin’s eyes. Have more men ride ahead and pick them off with arrows as they find them. It does not matter if some of the warriors fall trying to reach them. When our enemy is blind, we will find him more easily.’

Jelaudin stared into the distance, watching the flag signal as it rose and dipped four times.

‘The khan has taken the field,’ he said. His stomach clenched as he spoke and suddenly all the strength of his army seemed insubstantial. This was the man who had destroyed his father’s regiments, sent elephants mad with pain and carved his way through the golden cities. Jelaudin had known he would come, the knowledge tainting their victories. The khan’s pride demanded his presence and Jelaudin had known he would not be slow to follow.

‘How many men?’ Nawaz asked at his shoulder. He had not taken the time to learn the flag signals, but Jelaudin did not upbraid him.

‘Four tumans, that is forty thousand more warriors in the hunt. They will move faster now.’

For twelve days, they had led the Mongols into blind canyons and false trails, losing just a few men while they wound their way through the Afghan hills. The sudden withdrawal from Panjshir had always been a gamble, but Jelaudin knew the word would spread almost as fast as he could move his army. Cities waited for a thousand miles to hear that the khan’s men had been defeated. Jelaudin thought of them as he stared at the setting sun. They would rise when they heard. Those places where Mongol garrisons kept the peace would be at war again. Every day he remained alive weakened the khan’s grip on Arab lands. Jelaudin swore a silent oath as he stood there. He would shake it loose.