“I was puzzled by this,” she said. “As you said, it could have been a mistake, but now there was something that was making me wonder if something strange was going on. It seemed odd that the doctor should be so determined that I should not take blood pressure and then that he himself should go and make such a mistake. So I decided to carry out a little investigation myself. I have a friend who is a nurse too. She works in another clinic, and she had once told me that there was some old equipment lying about in a cupboard there. I asked her if there was a sphyg, and she said that she would look and see. When she reported back that there was one, I asked her if I could borrow it for a few weeks. She was a bit surprised, but she agreed.

“I hid the sphyg in my drawer at work. And then I waited for my chance, which eventually arrived. I had been paying attention to the medical records now, and each time I got them out for the doctor I looked to see whether it was a high blood pressure case. There were many of them, I noticed, and I began to wonder about them. All of them were on the same drug, which is quite an expensive one. We give them supplies of it from the clinic.”

Mma Ramotswe sat up, almost upsetting her cup of cold tea as she did so. “Now, Mma,” she exclaimed, “I think that I can already see what is happening here. The doctor is giving false blood pressure readings. He tells patients that they have high blood pressure when they really do not. Then he makes them take the expensive drug, which he provides for them. It must be a very good business for him.”

Boitelo stared at her. “No, Mma,” she said flatly. “That is not what is happening.”

“Then why did he enter the false reading? Why did he do that?”

“It must have been a genuine mistake,” said Boitelo.

Mma Ramotswe sighed. “But you said that you yourself were suspicious of it. You didn’t think it was a mistake.”

Boitelo nodded. “I didn’t,” she said. “You are right, Mma. I did not. But now I do. You see, I did two further tests. In each case it was while the doctor was busy with somebody else and there was one of these blood pressure patients in the waiting room. I took their blood pressure and then I compared the results I got with the results that the doctor later noted on their records.”

“And?”

“And they were the same.”