'There is a limit to the range of these monsters,' Taita encouraged the men. 'Nakonto knows their habits well. He says that as suddenly as we came upon them we will be free of them.'

Meren ordered forced marches and rode at the head of the column, setting a driving pace. Deprived of sleep and weakened by the venom that the flies pumped into their blood the men swayed in their saddles.

When a trooper collapsed his comrades threw him over the back of his horse and rode on.

Nakonto alone was inured to the insects. His skin remained smooth

and glossy, unmarked by stings. He allowed the insects to suck themselves full of his blood so that they could not fly. Then he mocked them as he tore off their wings: 'I have been stabbed by men, leopards have bitten me and lions clawed me. Who are you to annoy me? Now you can walk home to hell.'

On the tenth day after they had left the hills, they rode out of the fly country. It happened so suddenly that they were taken unawares. At one moment they were cursing and flogging at the whirling insects, then fifty paces further on the silence of the forest was no longer disturbed by the vicious whine. Within a league of passing out of the tyranny they came upon an isolated river pool. Meren took pity on the party. 'Fall out!' he roared. 'The last one into the water is a simpering virgin.'

There was a rush of naked bodies, then the forest rang with cries of relief and jubilation. When they emerged from the pool, Taita and Fenn ministered to everyone's swollen stings, smearing them with one of the magus's salves. That night the laughter and banter round the campfires was unstinted.

It was dark when Fenn knelt over Taita and shook him awake. 'Come quickly, Taitai Something terrible is happening.' She seized his hand and dragged him to the horse lines. 'It's both of them.' Fenn's voice cracked with distress. 'Windsmoke and Whirlwind together.'

When they reached the lines, the colt was down, his body heaving to the urgent tempo of his breathing. Windsmoke stood over him, licking his head with long strokes of her tongue. She reeled weakly as she tried to keep her balance. Her coat was standing on end and she was drenched with sweat: it dripped from her belly and ran down all four legs.

'Call Shofar and his troops. Tell them to hurry. Then run and ask them to fill their largest pot with hot water and bring it to me.' Taita's main concern was to get Whirlwind back on his feet and keep Windsmoke on hers. Once a horse was down it had lost the will to fight and surrendered to the disease.

Shofar and his men lifted Whirlwind and placed him on his feet, then Taita sponged him with warm water. Fenn stood at his head blowing softly into his nostrils, whispering encouragement and endearments while she persuaded him to eat one Tolas cake after another.

As soon as he had bathed the colt, Taita turned to Windsmoke.

'Be brave, my darling,' he murmured, as he wiped her down with a wet linen rag. Meren helped him to dry her vigorously with fresh cloths, and then they spread Taita's tiger-skin over her back. 'You and I will defeat this thing together.' He kept talking quietly to her, and used the

voice of power whenever he spoke her name. She cocked her ears to listen to him, splayed her legs and braced herself to keep her balance.

'Bak-her, Windsmoke. Do not give in.”

He hand-fed her the Tolas cakes, which he had dipped in honey. Even in her distress she could not resist this delicacy. Then he persuaded her to swallow a bowl of his special remedy for fever, yellow-strangler and equine distemper. He and Fenn joined hands to invoke the protection of Horus, in his form as the god of horses. Meren and his men joined in the prayers, and continued to chant them for the rest of the night. By morning, Windsmoke and her colt were still standing, but their heads were hanging and they would no longer take the cakes. They were, however, consumed by thirst, and drank eagerly from the pots of clean water that Fenn and Taita held for them. Just before noon Windsmoke raised her head and whickered to her colt, then staggered across to him and nuzzled his shoulder. He raised his head to look at her.

'He has lifted his head,' one man said excitedly.

'She stands more firmly,' another observed. 'She is fighting for herself and for her foal.'

'She has stopped sweating. The fever is breaking.'

That evening Windsmoke ate five more Tolas cakes with honey. The next morning she followed Taita down into the riverbed and rolled in the white sand. She had always favoured a particular variety of soft grass with fluffy pink seed heads that grew on the banks of the Nile, so Taita and Fenn scythed bundles of it and sorted from it the choicest stalks.

On the fourth day both Windsmoke and Whirlwind filled their empty bellies with it.

'They are out of danger,' Taita pronounced, and Fenn hugged Whirlwind, then wept as though her heart had broken and would never mend.

Despite the Tolas cakes, many other horses showed symptoms of the disease. Twelve died, but Meren replaced them from the small herd of salted animals. Some men were also suffering from the effects of the fly venom: they were racked with enervating headaches, and every joint in their bodies was so stiff that they could hardly walk. It was many more days before animals and men had recovered enough to resume the march.

Even then Taita and Fenn would not burden Windsmoke and Whirlwind with their weight, but rode spare horses and led them on their halter ropes. Meren reduced the length and pace of his daily marches to allow them all to recover completely. Then, over the days that followed, he increased the speed until they were moving briskly once more.

For two hundred leagues beyond the flies the land was devoid of human habitation. Then they encountered a small village of itinerant fishermen. The inhabitants fled as soon as the column of horsemen appeared. The shock of meeting these pale-skinned men with their strange bronze weapons, riding on strange hornless cattle, was too much for them. Taita examined their fish-smoking racks, and found them almost empty. The Nile no longer provided the village with her bounty.

Clearly the fishermen were starving.

On the floodplains along the riverbank herds of large, robust antelope, with scimitar horns and white patches around their eyes, were feeding.

The males were black, the females dark red. Meren sent out five of his mounted archers. The antelope seemed curious about the horses, and came to meet them. The first volley of arrows brought down four, and the next as many again. They laid out the carcasses on the outskirts of the village as a peace-offering, then settled down to wait. The starving villagers could not long resist and crept forward cautiously, ready to flee again at the first sign of aggression from the strangers. Once they had butchered the carcasses and had the meat grilling on a dozen smoky fires, Nakonto went forward to hail them. Their spokesman was a venerable greybeard, who replied in a squeaky treble.

Nakonto came back to report to Taita. 'These people are related to the Ootasa. Their languages are so similar that we understand each other well.'

By now the villagers were so emboldened that they came trooping back to examine the men, their weapons and horses. The unmarried girls wore only a string of beads round their waists, and almost immediately established friendships with the troopers who had no Shilluk camp followers.

The married women brought calabashes of sour native beer to Taita, Meren and the captains, while the elder, whose name was Poto, sat proudly beside Taita and readily answered the questions Nakonto put to him.

'I know the southlands well,' he boasted. 'My father and his father before him lived on the great lakes, which were full of fish, some so large it needed four men to lift them. Their girth was thus .. .' he made a circle with his skinny old arms '. .. and their length was thus…“ he jumped up and drew a line with his big toe in the dust, then took four full paces and drew a second line '. .. from there to there!'