Mma Ramotswe had not meant to embarrass her. Her question had not been a charged one, and she tried to set her at her ease. “I didn’t mean that,” she said. “I meant the old Africa, when there were fewer people without jobs. People had a place then. They belonged to their village, to their family. They had their lands. Now a lot of that has gone and they have nothing but a shack on the edge of a town. I do not like that Africa.”

Carla relaxed. “Yes. But we cannot stop the world, can we? Africa has these problems now. We have to try to cope with them.”

There was a silence. This woman has not come to talk politics, thought Carla; or African history. Why is she here?

Mma Ramotswe looked at her hands, and at the engagement ring, with its tiny point of light. “Ten years ago,” she began, “you lived out near Molepolole, at that place run by Burkhardt Fischer. You were there when an American called Michael Curtin disappeared in mysterious circumstances.”

She stopped. Carla was staring at her, glassy-eyed.

“I am nothing to do with the police,” said Mma Ramotswe, hurriedly. “I have not come here to question you.”

Carla’s expression was impassive. “Then why do you want to talk about that? It happened a long time ago. He went missing. That’s all there is to it.”

“No,” said Mma Ramotswe. “That is not all there is to it. I don’t have to ask you what happened, because I know exactly what took place. You and Oswald Ranta were there, in that hut, when Michael turned up. He fell into a donga and broke his neck. You hid the body because Oswald was frightened that the police would accuse him of killing Michael. That is what happened.”

Carla said nothing, but Mma Ramotswe saw that her words had shocked her. Dr Ranta had told the truth, as she had thought, and now Carla’s reaction was confirming this.

“You did not kill Michael,” she said. “It had nothing to do with you. But you did conceal the body, which meant that his mother never found out what happened to him. That was the wrong thing to do. But that’s not the point. The point is that you can do something to cancel all that out. You can do that thing quite safely. There is no risk to you.”

Carla’s voice was distant, barely audible. “What can I do? We can’t bring him back.”

“You can bring an end to his mother’s search,” she said. “All she wants to do is to say goodbye to her son. People who have lost somebody are often like that. There may be no desire for revenge in their hearts; they just want to know. That’s all.”

Carla leaned back in her chair, her eyes downcast. “I don’t know … Oswald would be furious if I talked about …”