Now, as they made their way through the outskirts of Mochudi, past the rash of small hairdressing establishments with their hand-painted grandiose signs, past the turn-offs that led to the larger houses of those who had made good in Gaborone and returned to the village, past the tax office and the general dealers, he said to her casually, almost as if he were thinking aloud, “I wouldn’t like to be one of his patients.”

“Of whose patients?”

“There was a doctor who worked at the hospital when I was there,” he said. “I didn’t like him. Nobody did. And I remember thinking: I would be frightened to be in that doctor’s care. I really would.”

She changed gear. A donkey had wandered onto the road and was standing directly in the path of the tiny white van. It was a defeated, cowed creature, and seemed to be looking directly up at the sun.

“That donkey is blind,” said Mr. Polopetsi. “Look at him.”

She guided the van round the static animal. “Why?” she said.

“Why does he stand there? That is what they do. That is just the way they are.”

“No,” she said. “That is not what I meant. I wondered what frightened you about him.”

He thought for a few moments before answering. “You get a feeling sometimes. You just do.” He paused. “Maybe we’ll see him.”

“Is he still there, Rra?”

Mr. Polopetsi shrugged. “He was last year. I heard from a friend. I don’t know if he has moved since then. Maybe not. He was married to a woman from Mochudi, so maybe he will still be there. He is a South African himself. Xhosa mother, Boer father.”

Mma Ramotswe was thoughtful. “Do you know many others from the hospital staff? From that time?”

“Many,” said Mr. Polopetsi.

Mma Ramotswe nodded. It had been a good idea, she decided, to bring Mr. Polopetsi with her. Clovis Andersen, author of The Principles of Private Detection, said in one of his chapters that there was no substitute for local knowledge. It cuts hours and days off an investigation, he wrote. Local knowledge is like gold.

Mma Ramotswe glanced at her modest assistant. It was difficult to think of Mr. Polopetsi in these golden terms; he was so mild and diffident. But Clovis Andersen was usually right about these things, and she muttered gold under her breath.

“What?” asked Mr. Polopetsi.

“We have arrived,” said Mma Ramotswe.