“Of course, if it’s an emergency,” she said hesitantly. “If one is heading somewhere to solve a crime, for example. Or taking a pregnant lady to the hospital. Then I think that it’s all right to go against the lights. As long as you’ve looked, of course.”

Mma Makutsi looked up the road. “Do you think that this is an emergency, Mma?”

“Well, writing threatening letters is a crime, I think,” said Mma Ramotswe. But she was not completely sure of that. She had a copy of the Botswana Penal Code in the office, which she occasionally waved at any client who might suggest doing something illegal—such as listening to the telephone calls of another—but was there anything in the code about threatening letters? There should be, she felt, but then there were many things that should be in the Botswana Penal Code but were not, because of some oversight on the part of the compilers—failing to support an indigent parent, for example, or conducting a loud telephone conversation on the verandah of the President Hotel when other people were trying to drink their tea in peace.

The lights changed, and they moved forward. Within a few moments they were in the parking area and she nosed the tiny white van into the nearest vacant space, switched off the ignition, and began to half run towards the supermarket entrance, accompanied by Charlie and Mma Makutsi.

“We must get a trolley,” said Mma Makutsi, as they entered.

“We must be careful to look like normal shoppers. Then we shall be able to see this person and observe her.”

“And then?” asked Charlie. “Should I detain her?”

Mma Makutsi scoffed. “You cannot detain people, Charlie. You are not a policeman! No, what we shall do is follow her and find out who she is. That’s what we should do, isn’t it, Mma Ramotswe?”

Mma Ramotswe had not thought that far. “I think so,” she said. “We will observe, I think.”

They moved towards the vegetable section. Charlie’s offer to push the trolley had been turned down by Mma Ramotswe, who thought it better for her to remain in control. Mma Makutsi walked beside her, one hand on the trolley bar.

“Do you mind if I pick up a few things as we go along?” asked Mma Makutsi. “I was going to have to come shopping later on, anyway. So I may as well get something for Phuti’s dinner while I’m about it.”

Mma Ramotswe agreed that this was a good idea. “But don’t spend too much time choosing,” she said. “She could almost have finished her shopping by now, and so we had better get down towards the end of the store as soon as possible.”