Mma Ramotswe shrugged. “It is difficult to say. Spells are nothing—they don’t exist. So how do you tell when there is nothing there—just air? Maybe somebody spoke to her. That is how people come to know about spells. People say, They have bought some bad medicine to use against you. That sort of thing.” She did not like to think about it; that was the old Africa, not the Africa of today, and certainly not the Botswana she knew. And yet it was there; just as it was elsewhere in the world, everywhere, really, where underneath the modern and the rational there ran a dark river of unreason and fear.

“The girl told her family,” Mma Ramotswe continued. “They said that they had feared something like this would happen. And they tried to keep her in the house. They did not like her to go anywhere except the school. At nights they all slept in the same room with the girl at the back, so that any person who came into the house would have to step over other sleepers before they came to the one they were looking for.

“The mother went quietly to a witch doctor and bought something to protect the girl. Some useless mixture of ground bones and leaves—they love that sort of thing—made into a paste. She put this on the girl’s cheeks, although the girl said that she did not believe in this nonsense. The mother said, ‘And when something bad happens, will you not believe in it then?’ And the girl said, ‘All of this is part of a world that has gone now. It is no longer true, any of this.’”

Mma Makutsi shook her head. “Poor girl.”

“Yes,” said Mma Ramotswe. “Because something bad did happen. She had an old aunt, this girl. Her parents said to her, ‘Do not visit your aunt now. Her place is far away. You will be in danger if you go.’

“The girl said that this was just superstition. ‘I am a strong girl,’ she said. ‘How can anything like that harm a strong girl in broad daylight?’ That is what she said, Mma, which is just the right thing for her to say. If more people said that sort of thing, then all this business could never flourish. It would die when it is out in the sun. It is a business that needs darkness and fear to stay alive.”

Their road was now almost deserted. It was lunchtime, and the sun was high in the sky overhead, casting short, vertical shadows. Before them, stretched out to the distant horizon on either side, was acacia-dominated scrub bush—mile upon mile of olive-green trees, like tiny umbrellas erected against the heat of the sun. And through the windows of the van, open to allow a draught of cooling air, came the noise of the cicadas, that high-pitched screeching that provided a constant background of sound for the African bush.