“Learn that there is nothing to be learned,” he said. “That boy is dead. He must have wandered off into the Kalahari and got lost. Gone for a walk and never come back. It’s easily done, you know. One thorn tree looks much like another, you know, and there are no hills down there to guide you. You get lost. Especially if you’re a white man out of your natural element. What do you expect?”

“But I don’t believe that he got lost and died,” said Mma Ramotswe. “I believe that something else happened to him.”

He turned to face her.

“Such as?” he snapped.

She shrugged her shoulders. “I am not sure exactly what. But how should I know? I was not there.” She paused, before adding, almost under her breath. “You were.”

She heard his breathing, as he returned to his chair. Down below, one of the students shouted something out, something about a jacket, and the others laughed.

“You say I was there. What do you mean?”

She held his gaze. “I mean that you were living there at the time. You were one of the people who saw him every day. You saw him on the day of his death. You must have some idea.”

“I told the police at the time, and I have told the Americans who came round asking questions of all of us. I saw him that morning, once, and then again at lunchtime. I told them what we had for lunch. I described the clothes he was wearing. I told them everything.”

As he spoke, Mma Ramotswe made her decision. He was lying. Had he been telling the truth, she would have brought the encounter to an end, but she knew now that her initial intuition had been right. He was lying as he spoke. It was easy to tell; indeed, Mma Ramotswe could not understand why everybody could not tell when another person was lying. In her eyes, it was so obvious, and Dr Ranta might as well have had an illuminated liar sign about his neck.

“I do not believe you, Rra,” she said simply. “You are lying to me.”

He opened his mouth slightly, and then closed it. Then, folding his hands over his stomach again, he leant back in his chair.

“Our talk has come to an end, Mma,” he announced. “I am sorry that I cannot help you. Perhaps you can go home and study some more logic. Logic will tell you that when a person says he cannot help you, you will get no help. That, after all, is logical.”

He spoke with a sneer, pleased with his elegant turn of phrase.