And that is the moment at which Charlie burst in. He did not knock, as even he normally did; he burst in.

“I’ve seen her,” he announced breathlessly. “I’ve just seen her.”

Mma Makutsi sniffed in an irritated way. “Seen who?” she snapped. “And have you forgotten how to knock, Charlie?”

Charlie ignored her and addressed his next remark to Mma Ramotswe. “That woman who brought the letter,” he said. “I have just seen her go into the supermarket. You seemed so interested in her that I rushed back to tell you. But since Mma Makutsi seems to be more concerned about knocking and such things perhaps I should not have bothered.”

Mma Ramotswe stood up. “Charlie,” she said, “we must go there now. You. Me. Mma Makutsi. Straightaway.”

THERE WAS NOT ENOUGH ROOM for all three of them in the tiny white van, and so Charlie crouched in the back, clinging on to the side, while Mma Ramotswe and Mma Makutsi occupied the driver’s and passenger’s seat, respectively. The van was making the suspicious knocking noise again, but that did not stop Mma Ramotswe from pressing the accelerator pedal flat to the floor. Even so, with the engine doing its utmost, there was no question of reaching such momentum as would break the speed limit, and Mma Ramotswe found herself glancing anxiously at her watch as they made their way along the Tlokweng Road in the direction of the Pick and Pay supermarket.

Fortunately the traffic, such as it was, was going in the opposite direction, streaming away from town, and there was little to hold them up. When they reached the lights at the southern edge of the village, the tiny white van was brought to a halt dutifully at the line.

“It’s a pity the lights are red,” said Mma Makutsi. “When you see detectives in films they do not let these things hold them up.”

Mma Ramotswe glanced from left to right. Everything was clear; there were no vehicles approaching.

“But it’s the law, Mma Makutsi,” she said. “You cannot have people deciding whether or not they will stop at lights. That is not the way we do things in Botswana—yet.”

“I was not saying that you should jump the lights, Mma,” said Mma Makutsi, somewhat huffily. “I do not jump the lights myself.”

“But you don’t drive,” observed Mma Ramotswe. “You can’t jump lights if you don’t drive.”

“When I am with Phuti,” said Mma Makutsi. “What I meant was that Phuti and I don’t jump lights. We always stop when the lights are red. Even when they are orange, we stop.”

Mma Ramotswe looked in both directions again. There was still nothing coming.