'It's starting, Ben.' His father seemed to echo his thoughts. 'It will only take one of those people to return to their home carrying the virus, and nobody will be able to stop it spreading. You have to make sure it doesn't happen.'

'How am I supposed to-?' Ben started to ask, but he cut himself short as his father emitted another of those deathly rattles from his lungs. 'Dad, are you OK?' he asked urgently.

But there was no reply. Russell Tracey had slipped once more into unconsciousness.

Ben bit his lip. All he wanted to do was to stay here, to look after his father. But that was not what his father had urged him to do. Gradually he became aware that the noise of the rain hammering on the roof had stopped, and Halima had approached and was standing just behind him. 'What should we do?' she asked.

Ben closed his eyes and breathed deeply and slowly in an attempt to regain his composure. 'Where is the next village?' he asked quietly.

'West of here,' Halima said. 'On the road Suliman took with us.'

'Is that the only road in?'

Halima nodded.

'And how far away is it?'

'Half a day's drive. Maybe a day because of the rains.'

'OK. There might still be time.' He chewed thoughtfully on the nail of his right thumb. 'I've got an idea,' he said. 'This is what we're going to do…'

Four thousand miles away, the same sun that was once more emerging over the rainforests of the Democratic Republic of the Congo was also beating down on the city of Macclesfield in Cheshire. Sam Garner, a bearded, bespectacled man in his mid-forties wearing a rather unfashionable short-sleeved shirt and a tie with soup stains down it, was glad of the air conditioning in his offices; but he was deeply concerned by the phone call he had just received. He had never met Russell Tracey's son, and didn't know if he was the sort of kid to pull practical jokes. But if his father was anything to go by, somehow he doubted it.

Sam had called the operator to try and trace where the call had come from, but there was nothing she could do to help. The more he thought about it, the more firmly he decided he had to take it seriously. It was too outlandish for a kid to make up, surely, and Ben had sounded genuinely fearful. But who should he call and who would listen and, even more importantly, be able to act on such meagre information? He twiddled with his pencil and tried to think things through calmly and logically. Sam Garner had seen the effects of the Ebola virus firsthand. He'd researched a small outbreak in the Central African Republic about three years ago, and he remembered thinking how much worse these diseases were in real life than in academic study. The people he had seen dying of the virus had ended their lives in terrible pain. At the time he remembered being thankful that you could only catch Ebola if you came into contact with the bodily fluids of infected sufferers. Humans had never caught it through airborne transmission, though monkeys possibly had. A slight mutation, and Ebola could turn into a health threat the like of which the world had never seen.

It had become something of an obsession of Sam's. There was no doubting that there were millions of organisms out there unknown to modern science, microscopic bacteria and viruses living in tiny undiscovered colonies with their own quirks and characteristics. You didn't need to be an amazing scientist to work out that with so many millions of possibilities, it was not only likely that someone someday would stumble across a new virus as invasive as Ebola but much more contagious. It was inevitable. Sam had even developed his own system of grading virus threats.

Code Green: no threat.

Code Amber: discovery of reservoir and suspected threat to human life.

Code Red: widespread infection and threat of major epidemic.

Sometimes Sam's colleagues made fun of him and the way he had taken to lobbying governments and NGOs, getting up on his soapbox and arguing the need for more funding in this arena; but Sam didn't care. He knew what he thought, and he knew one day he would be vindicated in some horrific way.

Perhaps that day had come. Or perhaps Russell Tracey and the villagers of this unheard-of place in the DRC had succumbed to something totally different. All Sam knew was that what Ben had described was perfectly possible, if unthinkable, and that Russell Tracey was not the sort of man to overstate his case. If Russell thought this was a Code Red situation, it probably was.

But his thought processes simply led him back to square one: who would be the best person to notify? Who might act promptly based on no real data? But if this really was a Code Red…

He had an idea. Clearing an unruly pile of papers from his desk with a sudden sweep of his arm, he pulled the keyboard of his computer towards him and directed his Internet browser to a search engine with a light tap of his fingers. Within seconds he had directed himself to the United Nations website. His eyes scanned quickly over the screen until he saw the link he was looking for: 'PEACE & SECURITY'. He navigated to the peacekeeping section of the website, then found the link for 'CURRENT OPERATIONS'. A drop-down menu directed him to ' AFRICA ' and then 'MONUC (DEM. REP. OF THE CONGO)'. A few clicks later, he found himself scribbling down the number of the main office in Kinshasa of the UN Mission in the DRC.

Then he stopped.

What were they going to think, these people, when he phoned them out of the blue to alert them to a deadly virus in an unheard-of backwater of the country? What would he think, if someone he had never heard of called him up to say that half the population of Britain might die if he didn't quarantine Macclesfield? If ever there was a long shot, this was it. Sam Garner knew he was going to have to be very convincing.

He dialled the number.

'Oui, bonjour,' a woman's voice answered almost immediately.

'Do you speak English?'

'Yes, sir, a little.'

'Good.' Sam spoke slowly and clearly. 'My name is Dr Sam Garner. I'm calling from England and I am a specialist in infectious diseases. You're going to have to listen to me incredibly carefully…'

CHAPTER NINETEEN

'When will you be coming home, Daddy?'

The thin child who looked up at her equally emaciated father was eight years old, with large dark eyes and tightly curled hair. She didn't want her father to leave.

'In two weeks,' he said gruffly, softening only when he saw the tears welling up in his daughter's eyes. He knelt down and took her hand. 'The men say there is work in the next village. When I come back, I will have a little money. Enough, maybe, to buy some meat for us. You must look after your mother while I am gone. Do you think you can do that for me?'

The little girl nodded bravely. Her father smiled at her, stroked the side of her head, then stood up. His wife was standing in the corner of the hut, obscured somewhat by the shadows. He nodded cursorily at her, then left.

Outside, the minibus was waiting. It was an old bus, like every vehicle the man had ever seen, with rust patches and mismatched wheels. And it was almost full. He hurried towards it, not wanting to risk missing his seat. The smiling men who had flown in from Kinshasa the previous day had told him that this was a limited opportunity for work, that if they wanted to earn some of the money that was available, they needed to sign up now and leave tomorrow. Little did anyone know that they would be back to transport another busload of workers as soon as possible.

Quietly the man took his place at the front of the bus. It was hot and smelly, and filled with men who, like him, had faces that reflected the hardship of their lives, yet now showed hope that they might be able to earn the money they so desperately needed to support their families.