The woman looked at the bottle, then back at Ben. There was a wariness in her eyes, but she did not refuse the gift, simply nodding her head in a curt gesture of appreciation. Then she turned and walked quickly away.

Ben watched her go. Gradually he became aware of Abele standing just behind him. 'You will not be able to give charity to everyone who is sick in this village, Ben,' he murmured.

Ben didn't take his eyes off the woman. 'I thought you said you were going to stay in the compound, Abele,' he retorted, beginning to feel a bit irritated by his constant cryptic comments.

Abele remained stony-faced. 'I am here to look after you,' he said shortly.

'Come on, then.' The woman was turning round a corner, so Ben ran after her with Abele running reluctantly behind. He was beginning to have a suspicion, and he wanted to see if he was right.

Sure enough, as he turned the corner, he saw the woman opening the wooden door to a shabby- looking hut. Looking over her shoulder, she saw Ben, but she quickly pulled her gaze away, stepped inside and slammed the door shut. Ben approached. Painted on the door in thick red paint – just as it had been at Halima's house – there was a cross. 'That's what it means, isn't it?' Ben asked breathlessly. 'They paint a red cross when someone is dying in the house.'

'Or has died,' Abele noted darkly.

Ben walked away from the house, checking the doors of the other huts in this ramshackle street. Red crosses adorned the fronts of almost half of them. 'What's wrong with all these people?' he breathed, his head suddenly spinning at the thought of so much death. He turned to Abele.

His face made it clear he had nothing to say on the subject; he just fingered the charm that hung around his neck.

Suliman had not accompanied Russell into the deepest part of the mine; it had not been necessary. As mine manager he had to attend to the workers excavating for tin elsewhere, so he had left the scientist in the hands of one of his colleagues, a rather surly villager who spoke no English but seemed very nervous as he held a torch to the exposed rock face positioned just by the underground lake from which Russell was taking his samples. It was hard work and Russell was soon damp with sweat despite the fact that it was cool in the caves. He would have liked to splash water from the lake over his face, but he knew how foolish that would be: cholera, tapeworms – it could be hiding all manner of parasites and diseases.

It was unusual to find Coltan down here. It was normally surface-mined, but there had been instances of it being discovered as an offshoot of other mining operations. And of course it would take him a while to do all the proper tests at his lab back in the UK, but he could already tell that this was a rich source of the good stuff, and he would be able to give his findings to Kruger and the others back in Kinshasa. That would please them, and at least he would feel as if one part of his excursion into Africa with Ben had gone the way it should. Russell had to admit that things hadn't really been going according to plan. If Ben seemed jumpy around everyone, it wasn't really much of a surprise. He was only a young boy, after all, and all things considered, his father thought he was coping quite well. If only he hadn't seemed so openly suspicious of Kruger and Suliman, two men who seemed to be doing their very best to make everything run smoothly.

Ah well, Russell thought to himself. That sort of maturity will come. In time.

He glanced at his watch in the torchlight. It was getting on, so he turned and nodded to his companion with a smile. 'We'll finish now,' he said in loud, overly pronounced tones that he knew the guy wouldn't understand, but he hoped he would get his drift.

The man nodded and turned round, eager to leave. 'I still need the light here!' Russell called, spinning round and grabbing him by the arm. The man uttered some harsh words in a deep voice, pulling his arm away from Russell, his face sinister and demonic by the light of the torch. As he lowered the torch, something caught Russell's eye. 'Shine it there,' he instructed, pointing out over the water. His companion did as he was told. A small animal – a bat, most likely, Russell thought – was flailing in the water, struggling.

And then, quite suddenly, it fell silent.

Its death seemed to bring an increased chill into the cave. Russell dragged his attention away and packed up his things, and the two of them started walking along the rickety wooden flooring that would eventually lead them out of the mine. They trudged along in silence, the black man holding the torch, Russell keeping his eyes firmly on the potentially treacherous ground.

As they were leaving the cave, he saw another dead bat, right in front of him, its body already decaying.

He said nothing, but his scientist's brain started ticking over. Clearly there was a colony down here somewhere, a great many of them, no doubt. With such a large population, the probability of seeing dead individuals was high. He smiled to himself. There was something satisfying about seeing statistics in action.

Had he directed the beam back across the water, however, Russell might have noticed a small opening into an adjoining cave. He could never have reached it to explore, even if he had wanted to, because the only way of accessing it was across the water. Had he been able to, however, he would have been horrified by what he saw on the banks of the underground lake.

Thousands upon thousands of bats.

All of them dead.

All of them piled high in a mountain of increasingly rotten and stinking flesh.

Ben's dad returned to the compound later that afternoon. Abele had insisted that he and Ben should go back, and Ben's recent discovery that half the huts in the village seemed to be housing the sick and dying had dampened his enthusiasm for exploring, so he had sought shelter from the heat and the increasingly intolerable humidity by lying on his bed in the half darkness. Now, though, it was beginning to cool down.

Russell looked grimy and tired – more tired than Ben had seen him in a long time in fact, with large, black rings under his eyes and a faintly haggard expression. He entered the compound with Suliman sticking close to him. Both men had sweat on their bald heads, though Suliman looked more comfortable with it than Russell.

'Good day?' Ben asked his dad.

Russell nodded. 'It's a rich source of good-quality Coltan. I need another day there, and then we can get back.' He turned to Suliman. 'Thank you for your kindness today,' he said politely. 'Same time tomorrow?'

'My people will be here to collect you.' Suliman bowed slightly, and made to leave.

'Just a minute!' Ben said sharply. 'I want to ask you a question.'

Suliman turned, and Ben felt both men's eyes on him.

'What's making everyone so ill? Why is everyone dying?'

'Ben!' Russell reprimanded. 'I don't want to hear you speaking to our hosts so rudely.'

'It's true, Dad. Every other house in this village has a red cross painted on the door. It means that someone is dying, or has died recently, in that house. We've been brought here without being told – I think we deserve to know what's going on.'

Suliman looked intently at him, his face hard before it suddenly dissolved into a softer smile. 'It's true, Ben,' he whispered, his rasping voice sounding almost snakelike. 'Many of our villagers are sick. You are taking your malaria medication, I hope?'

Ben nodded mutely.

'Good. It has been bad lately. A very vicious strain. The dead are as numerous as those who survive it. Few people can afford the medicine.'

Ben said nothing; malaria was a big problem in the area, that much he knew, and Suliman's explanation had the desperate ring of truth.