'Ride straight to the marker, round it and ride back again. The start line is also the finish line,' Umar said. Neither rider nodded this time. They knew the course. Both had been over it during the day.

'The starting signal will be a blast on Tarlq's horn. The minute you hear it, you may start.'

Tariq, an elder of the tribe, stepped forward with a large brass horn. He brandished it so they could both see it. Earlier in the day, Will had been made familiar with the note of the horn.

'In your hands, Tariq, and in God's will,' Umar intoned. It was the official notice that the next sound to be heard would be the starter's horn. An expectant silence fell over the crowd. Somewhere, a child started to ask a question. Umar looked round angrily and the mother quickly silenced her offspring. Umar gestured to Tariq and the older man raised the large, bell-mouthed horn to his lips.

Will watched him intensely. He saw the Bedullin's chest swell as he took a deep breath. Beside him and slightly behind him, he knew, Hassan would be watching like a hawk.

He tightened his grip on the reins, forced himself to relax his legs around Tug's body. He didn't want to send any inadvertent signal to the horse before it was time.

Now!

The horn brayed its metallic baritone note and he squeezed Tug with his knees. Dimly, he heard Hassan's yelled Yaaah! as he urged Sandstorm forward. The crowd roared with one huge voice. Then the sound cut off in shock.

Tug shot away from his stiff-legged stance like an arrow, going from stock-still to full gallop in the space of a few metres. Sandstorm, excited and prancing, was left behind, curvetting and tossing his head for the first few paces. Then Hassan clapped his heels into the palomino's sides and he stretched out in a gallop after Tug.

The crowd, silenced momentarily by Tug's incredible acceleration from a standing start, began yelling again, screaming for Hassan and Sandstorm to run him down.

Even Will, who was aware of Tug's phenomenal ability to accelerate, was a little surprised at the lead they had established already. He knew that Sandstorm would overhaul them before long. Once he was in stride, the Arridi was definitely faster than Tug over a kilometre or two. But now he hoped the shock of being left behind at the start would force Hassan to overstretch his mount, using up some of the precious energy reserves that would become so important in the last few kilometres.

Behind him, vaguely, he could hear the yelling tribesmen. Closer to, he heard the rolling thunder of Sandstorm's hooves on the rocky ground. Tug's ears were up and his legs were churning, throwing a plume of sand and dust into the air behind them.

Will touched his neck.

'Take it easy, boy. Pace yourself.'

Tug's head tossed fractionally in response. Not too much as he didn't want to lose stride or balance as he did so. Will felt him ease a little and nodded. Sandstorm's hooves were closer behind him now. The Arridi horse was as fast as lightning, he thought.

Hassan, a few metres behind them, was worried. He had no idea how fast the foreign horse would be. The horse's lines and configuration gave no hint of his startling off-the-mark speed. And even now that Sandstorm was gaining, he was doing so much more slowly than Hassan would have liked. He urged the horse to give a little more and heaved a sigh of relief as he began to draw alongside the foreigner and the shaggy little grey. The other rider didn't turn his head to look at them but Hassan saw the horse's eye rolling to view them as they came alongside.

Fast horses hate being led in a race. And this was definitely a fast horse – not as fast as Sandstorm but faster than he had expected. In Hassan's experience, once a horse found itself overtaken and led by another, it would often give in – or overextend itself, trying desperately to regain the lead. Hassan knew it was time to establish his horse's superiority. He flicked the reins against Sandstorm's neck and the palomino found another few metres of speed. He surged forward, away from Tug.

Will felt Tug begin to respond and for the first time he could remember, he checked him firmly with the rein. Tug snorted angrily. He wanted to show this flashy Arridi horse what racing was all about. But he obeyed Will's touch, and denied his own instinctive urge to go all out.

'Not yet, boy,' he heard Will's voice. 'Long way to go.'

They flashed past the two-kilometre mark, hearing the cheers of the marshals stationed there as they went. The cheers were all for Sandstorm, who was now leading Tug by nearly forty metres. The Arridi horse ran beautifully, Will thought grimly, with a long, powerful stride and perfect rhythm. Forty metres was far enough, he thought. He signalled Tug to increase his pace a little and Tug responded. Will felt a surge of affection for the horse under him. Tug would keep running like this all day, he knew. He wondered if Sandstorm could do the same.

He estimated that they had picked up five to ten metres when Hassan and Sandstorm rounded the halfway marker. Comfortably in the lead, Hassan had eased his horse's pace a little, knowing that his best turn of speed was behind them now.

He waved as they passed the other rider and horse. There was no response from Will, and Hassan grinned behind his kheffiyeh. He wouldn't wave if he were losing, either, he thought.

Round the halfway marker, Tug's hooves clattered on the stony ground, skidding slightly as they turned and set out after Sandstorm. They'd picked up a little distance when Sandstorm turned, lost it again when they followed suit. Maybe less than thirty metres between them now.

'Go now, Tug!' Will yelled and the horse dug deep into his reserves of strength and endurance and courage and accelerated under him. Will could see Sandstorm through the cloud of dust and sand he was kicking up – appropriate name, he thought grimly. The palomino's flanks were streaked with sweat and his sides heaving with exertion. Slowly, Tug narrowed the gap to the Arridi horse. With two kilometres to go, he moved alongside, the two horses plunging side by side, each head alternately taking the lead, losing it, taking it again as they raced stride for stride, neither gaining on the other.

There would be a moment, Will knew, when it was time for the final sprint. Both horses and both riders were aware of it. It was a matter of perfect timing. Too soon and the horse would be exhausted before the finish line. Too late and the race would be lost.

The horses, side by side, glared at each other, their eyes rolling in their heads, whites showing so each could view the enemy. Then Tug surged ahead and Will couldn't check him – to do so now would be to lose speed and Tug had cast the dice for them, sensing the moment. He moved a neck length, then a body length, ahead of Sandstorm, moving faster than Will could ever remember him doing. The drumming of the horses' hooves filled his consciousness. Then he heard Hassan yelling encouragement to Sandstorm and, turning his head slightly, he saw the Arridi horse begin to regain ground on them. Unbelievably, he was overhauling Tug yet again.

Then Tug faltered.

It was the slightest break in rhythm and pace but Will felt it and knew it was all over. Sandstorm saw it too and lunged ahead of them, a metre… two… five… the clods of dirt and sand flew up in Will's face, stinging the small area of skin exposed around his eyes, forcing him to grit his eyes almost shut.

There were three hundred metres to go and Sandstorm was fifteen metres ahead of them. Tears blurred Will's vision as he realised he had lost the race – and his horse.

He knew he could ask Tug for more. He could urge him to try to catch up. And he knew the little horse would respond until the effort killed him. Tug had already hit the wall. Sandstorm's pace had been too much. The early lead it had given him had been too great. He was twenty metres ahead of them.