Ala-ud-Din beckoned to three sons of chieftains riding behind his elephant. He saw his son Jelaudin riding close, his young face stern with righteous anger. Ala-ud-Din raised a proud hand in greeting as the scouts came up.

‘Take my orders to the front,’ he told them. ‘Have the flanks move out to a wider line. Wherever the enemy strikes, we will surround them.’

‘Master,’ Abbas said. The servant had paled. ‘They are already attacking.’

‘What?’Ala-ud-Din snapped. He narrowed his eyes, blinking in surprise at how close the Mongols had come. He could hear distant shouts as his front ranks met the first volleys of arrows with raised shields.

Columns of galloping Mongol horsemen were swinging in, passing the front and riding along the vulnerable flanks of his army. Ala-ud-Din gaped. Khalifa could have held them, but the man had betrayed his master. He could feel his son’s eyes burning into him, but he would not send the guard out yet. They were his shield and they rode the only horses he had left.

‘Tell the generals that we do not stop for these. March on and use the shields. If they come too close, make the sky black with arrows.’

The noble sons raced to the front and the shah fretted as the elephant strode on, oblivious to its master’s concerns.

Tsubodai rode at full gallop along the flank of the shah’s army. He stood in the stirrups with his bow bent, balancing against the pony’s rhythms. He could feel the strike of each hoof and then there would be a moment of flying stillness as all four legs were in the air. It lasted for less than a heartbeat but he loosed an arrow in that instant and watched it strike a yelling enemy soldier, knocking him off his feet.

He could hear the shah’s officers bark commands, strange syllables on the wind. The man himself was well protected in the heart of the army. Tsubodai shook his head in amazement at the core of riders trapped in the centre. What good did they do there, where they could not manoeuvre? The elephants too were deep in the ranks, too far to hit with his shafts. Tsubodai wondered if the shah valued them more than his own men. It was one more thing to know. As he thought and rode, thousands of marching men raised their double-curved bows and loosed. Arrows whined at him and Tsubodai ducked instinctively. The shah’s bows had more range than anything he had faced in Chin lands. Tsubodai had lost men on his first pass down the flank, but he could not stay out of reach and still make his own shafts count. Instead, he brought his column swinging in, pounding the Arabs with arrows, then galloping away as the reply came snapping back at him. It was a risky manoeuvre, but he had begun to get a feel for how long he could delay in order to aim. The Arabs had to hit a fast-moving column, while his men could aim anywhere in the mass.

Around him, his minghaans adopted the tactic, each column of a thousand biting holes in the Arab lines before racing clear. The shah’s army marched on and, though the shields saved many, a trail of broken dead marked their path towards the pass in the hills.

Tsubodai pulled his men in a wider curve than the last three strikes, straining his eyes to see the pass. Once the shah’s front ranks reached it, there would be no chance to slip back in and join Kachiun. The shah’s army advanced like a plug being forced into a bottle and there was not much time left before the pass was blocked. Tsubodai hesitated, his thoughts spinning. If the shah continued at that speed, he would leave the flying columns behind and punch his way through to Otrar. Kachiun’s four thousand would surely not stop such a mass. It was true that Tsubodai could continue the attacks on the rear as they advanced and he knew that was a sound decision. He and his men could snatch thousands from the helpless ranks and the shah would be unable to stop them. Even then, there were two other passes to go round the army. Tsubodai could lead the minghaans through and still support Genghis at Otrar.

It was not enough. Though the Mongol riders had killed thousands, the shah’s army barely shuddered as they closed ranks over the dead and moved on. When they reached the plain before Otrar, Genghis would be left with the same problem Tsubodai had been sent to solve. The shah would hit the khan from the front, while the Otrar garrison waited at his back.

Tsubodai led his men in once more, loosing arrows a thousand at a time. Without warning, another minghaan crossed his path and he was forced to pull up or crash into the young fool who led them. Arrows soared out of the shah’s ranks as soon as they saw him slow and this time dozens of warriors fell, their horses screaming and bloody. Tsubodai swore at the officer who had ridden across his line and caught a glimpse of the man’s appalled expression as the two forces separated and swung away. It was not truly his fault, Tsubodai acknowledged. He had trained his own tuman for just such an attack, but it was hard to weave trails around the shah without some confusion. It would not save the man from public disgrace when Tsubodai caught up with him later on.

The shah’s army reached the pass and Tsubodai’s chance to dart in ahead of them had gone. He looked for Jelme, knowing the older general was riding his own weaving path, but he could not see him. Tsubodai watched the tail of the great host begin to shrink as the shah passed to what he thought was safety. If anything, the stinging attacks on the flanks intensified as the minghaans had less ground to cover. As the tail shrank, they struck again and again and Tsubodai saw some of the wilder men lead attacks with swords, cutting right into the marching lines. The Arabs screamed and fought, holding them off as best they could, but with every pace the numbers fell in Tsubodai’s favour. There would be a moment when the flying columns outnumbered those left in the tail and he decided then to cut it off completely.

He sent his freshest men off to pass on the order, but it was hardly necessary. The Mongols had gathered round the last of the shah’s army, harrying them so closely that they had almost stopped. The ground was red around the mouth of the pass and Tsubodai saw limbs and bodies lying everywhere as the carnage grew.

Forty thousand Arabs were still in the column before the pass when a shudder rippled through them. Tsubodai cocked his head and thought he could hear screams in the distance, echoing back from the hills. Kachiun’s attack had begun. Tsubodai’s quiver was empty on his back and he drew his sword, determined to see the shah’s tail wither in the sun.

Warning shouts broke his concentration as Tsubodai led his men in again, this time directly across the face of the column. He had chosen a spot close to the pass itself and his heart was hammering as he kicked his mount into a gallop. At first, he did not hear the shouts, but his instincts were good and he looked up for the source, raising his sword to halt his men before the attack.

For an instant, Tsubodai swore under his breath. He could see riders and an awful suspicion followed that the shah had kept a rearguard to surprise their attackers at just such a moment. The fear passed as quickly as it had come. He saw his own people riding and his heart lifted. Jochi still lived and Jebe rode with him.

Tsubodai looked around sharply with fresh eyes. Perhaps thirty thousand Arabs still struggled to reach the pass, hammered and struck on all sides. The minghaans really did swarm around them like wasps, Tsubodai thought, but even a bear could be brought down in the end. He was not needed there, though he could not leave without telling Jelme.

It seemed to take an age before he found his fellow general, bloody and battered, but jubilant as he too readied his men to ride in once more.

‘Like sheep to a slaughter!’ Jelme shouted as Tsubodai rode up. Concentrating on the battle, he had not yet seen the riders and Tsubodai only nodded in their direction.