Mma Makutsi arrived at the house early. She had been invited for six o'clock, and arrived at ten to six. “It is always polite to arrive early,” she said. “I have read that ten minutes is about right.”

Mma Ramotswe looked doubtful. She read the same magazines as did Mma Makutsi, and she was sure that the advice she had seen was the direct opposite of what Mma Makutsi had just claimed. She would have to be careful, though, as Mma Makutsi did not always welcome contradiction or correction. In fact, she never welcomed either of these.

“I am not sure,” said Mma Ramotswe as she ushered her visitor into the kitchen. “Are you certain that it's not, perhaps, a little bit the other way round? I'm not sure, of course, Mma. But why would they tell you to arrive early?”

“Because it's polite,” said Mma Makutsi. “That is why, Mma. There are some things that are polite, and there are some things that are rude. It is polite to arrive ten minutes early.”

Mma Ramotswe pursed her lips. Mma Makutsi might be a person of firm views, and she might be somebody whom one would normally treat with great care, being slightly given to explosive reactions, but was it right to allow her to go through life believing something so clearly misguided as this? Mma Ramotswe thought not.

“Well, Mma, perhaps we should just think about it a bit.”

“No need,” said Mma Makutsi firmly, lowering herself onto a chair at the kitchen table. “The rules of good behaviour are firm, Mma, as you well know. We know that it is wrong to take a present with one hand—we know that. It is just there, that rule, at least in Botswana. There may be countries where they have not heard of this—I know that—but I am not talking about such places. I am talking about Botswana. We cannot question these things.”

Mma Ramotswe took a pan down from the shelf. “Yes,” she said. “You are right, Mma, about these things. I would never say that you are wrong.”

“Good,” said Mma Makutsi.

“But at the same time,” Mma Ramotswe went on, “it is possible to look at these rules and see what lies behind them. That tells us why they exist. The reason for the rule against taking a present with one hand is that it looks as if you don't really appreciate the present—that you can only be bothered to use one hand to take it. That is why that one is there.”

Mma Makutsi was silent.

Mma Ramotswe took the opportunity to continue. “And the rule about calling out Ko, ko before you go into a person's house is also there for a reason. If you do not call out in that way, then you may find the person who lives in the house without their clothes on or busy with something else. You never know what you will see in another person's house.”

Again Mma Makutsi said nothing. Emboldened, Mma Ramotswe moved on to the subject of arriving early. “Now, if we think about the rule as to when you should arrive …”