Mma Ramotswe was about to laugh at the suggestion. “Oh no,” she began. But then she stopped herself, and the thought occurred to her that perhaps this was exactly what they were letting themselves in for. Tati Monyena had described the deaths as mishaps and had hinted, at the most, that there was some form of unexplained negligence behind them; he had said nothing about deliberate killing. And yet it was possible, was it not? She remembered reading somewhere about cases where hospital patients had been deliberately killed by doctors or nurses. She thought hard, probing the recesses of her memory, and it came to her. Yes, there had been such a doctor in Zimbabwe, in Bulawayo, and she had read about him. He had started to poison people while he was still at medical school in America and had continued to do so for years. These people existed. Was it possible that a person like that could have slipped into Botswana? Or could it be a nurse? They did it too sometimes, she believed. It gave them power, somebody had said. They felt powerful.

She half-turned to Mr. Polopetsi. “I hope not,” she said. “But we must keep an open mind, Rra. It is possible, I suppose.”

They were ten miles from Mochudi now, and Mma Ramotswe spent the rest of the journey describing to Mr. Polopetsi what Tati Monyena had told her: three Fridays, three unexplained deaths, and all in the same bed.

“That cannot be a coincidence,” he said, shaking his head. “That sort of thing just does not happen.” He paused. “You know that I worked in this hospital once, Mma Ramotswe? Did I tell you that?”

Mma Ramotswe knew that Mr. Polopetsi had worked as an assistant in the pharmacy at the Princess Marina Hospital in Gaborone, and she knew of the injustice that occurred there which led to his spell in prison. But she did not know that he had been at Mochudi.

“Yes,” Mr. Polopetsi explained. “I was there for eight months, while they were short-staffed. That was about four years ago. I was in the pharmacy.” He lowered his voice as he mentioned the pharmacy, in shame, she thought. All that had turned sour for him, and all because of a lying witness and the transfer of blame. It was so unfair, but she had gone over all that with him before, several times, and she knew—they both knew—that they could do nothing to remedy it. “You are innocent in your heart,” she had said to him. “That is the most important thing.” And he had thought about that for a few moments before shaking his head and saying, “I would like that to be true, Mma, but it is not. It is what other people think. That is the most important thing.”