The blue car was taking its time, and Mma Ramotswe did not have to strain to keep up. They drove past the Sun Hotel and made their way towards the Stadium roundabout. There they turned in towards town and drove past the hospital and the Anglican Cathedral towards the Mall. Shops, thought Mma Ramotswe. They're just going shopping; or are they? She had seen teenagers meeting one another after school in places like the Botswana Book Centre. They called it "hanging around," she believed. They stood about and chatted and cracked jokes and did everything except buy something. Perhaps Nandira was going off to hang around with this Jack.

The blue car nosed into a parking place near the President Hotel. Mma Ramotswe parked several cars away and watched as the two girls got out of the car, accompanied by an older woman, presumably the mother of the other girl. She said something to her daughter, who nodded, and then detached herself from the girls and walked off in the direction of the hardware stores.

Nandira and her friend walked past the steps of the President Hotel and then slowly made their way up to the Post Office. Mma Ramotswe followed them casually, stopping to look at a rack of African print blouses which a woman was displaying in the square.

"Buy one of these Mma," said the woman. "Very good blouses. They never run. Look, this one I'm wearing has been washed ten, twenty times, and hasn't run. Look."

Mma Ramotswe looked at the woman's blouse-the colours had certainly not run. She glanced out of the corner of her eye at the two girls. They were looking in the shoe shop window, taking their time about wherever they were going.

"You wouldn't have my size," said Mma Ramotswe. "I need a very big blouse."

The trader checked her rack and then looked at Mma Ramotswe again.

"You're right," she said. "You are too big for these blouses. Far too big."

Mma Ramotswe smiled. "But they are nice blouses, Mma, and I hope you sell them to some nice small person."

She moved on. The girls had finished with the shoe shop and were strolling up towards the Book Centre. Mma Ramotswe had been right; they were planning to hang about.

THERE WERE very few people in the Botswana Book Centre. Three or four men were paging through magazines in the periodical section, and one or two people were looking at books. The assistants were leaning over the counters, gossiping idly, and even the flies seemed lethargic.

Mma Ramotswe noticed that the two girls were at the far end of the shop, looking at a shelf of books in the Setswana section. What were they doing there? Nandira could be learning Setswana at school, but she would hardly be likely to be buying any of the schoolbooks or biblical commentaries that dominated that section. No, they must be waiting for somebody.

Mma Ramotswe walked purposefully to the African section and reached for a book. It wasThe Snakes of Southern Africa, and it was well illustrated. She gazed at a picture of a short brown snake and asked herself whether she had seen one of these. Her cousin had been bitten by a snake like that years ago, when they were children, and had come to no harm. Was that the snake? She looked at the text below the picture and read. It could well have been the same snake, because it was described as nonvenomous and not at all aggressive. But it had attacked her cousin; or had her cousin attacked it? Boys attacked snakes. They threw stones at them and seemed unable to leave them alone. But she was not sure whether Putoke had done that; it was so long ago, and she could not really remember.

She looked over at the girls. They were standing there, talking to one another again, and one of them was laughing. Some story about boys, thought Mma Ramotswe. Well, let them laugh; they'll realise soon enough that the whole subject of men was not very funny. In a few years' time it would be tears, not laughter, thought Mma Ramotswe grimly.

She returned to her perusal ofThe Snakes of Southern Africa. Now this was a bad snake, this one. There it was. Look at the head! Ow! And those evil eyes! Mma Ramotswe shuddered, and read: "The above picture is of an adult male black mamba, measuring 1.87 metres. As is shown in the distribution map, this snake is to be found throughout the region, although it has a certain preference for open veld. It differs from the green mamba, both in distribution, habitat, and toxi-city of venom. The snake is one of the most dangerous snakes to be found in Africa, being outranked in this respect only by the Gaboon Viper, a rare, forest-dwelling snake found in certain parts of the eastern districts of Zimbabwe.

"Accounts of attacks by black mambas are often exaggerated, and stories of the snake's attacking men on galloping horses, and overtaking them, are almost certainly apocryphal. The mamba can manage a considerable speed over a very short distance, but could not compete with a horse. Nor are the stories of virtually instantaneous death necessarily true, although the action of the venom can be speeded if the victim of the bite should panic, which of course he often does on realising that he has been bitten by a mamba.

"In one reliably recorded case, a twenty-six-year-old man in good physical condition sustained a mamba bite on his right ankle after he had inadvertently stepped on the snake in the bush. There was no serum immediately available, but the victim possibly succeeded in draining off some of the venom when he inflicted deep cuts on the site of the bite (not a course of action which is today regarded as helpful). He then walked some four miles through the bush to seek help and was admitted to hospital within two hours. Antivenom was administered and the victim survived unscathed; had it been a puff-adder bite, of course, there would have been considerable necrotic damage within that time and he may even have lost the leg…"

Mma Ramotswe paused. One leg. He would need to have an artificial leg. Mr Patel. Nandira. She looked up sharply. The snake book had so absorbed her that she had not been paying attention to the girls and now-where were they?-gone. They were gone.

She pushedThe Snakes of Southern Africa back onto the shelf and rushed out into the square. There were more people about now, as many people did their shopping in the latter part of the afternoon, to escape the heat. She looked about her. There were some teenagers a little way away, but they were boys. No, there was a girl. But was it Nandira? No. She looked in the other direction. There was a man parking his bicycle under a tree and she noticed that the bicycle had a car aerial on it. Why?

She set off in the direction of the President Hotel. Perhaps the girls had merely gone back to the car to rejoin the mother, in which case, everything would be all right. But when she got to the car park, she saw the blue car going out at the other end, with just the mother in it. So the girls were still around, somewhere in the square.

Mma Ramotswe went back to the steps of the President Hotel and looked out over the square. She moved her gaze systematically-as Clovis Andersen recommended-looking at each group of people, scrutinising each knot of shoppers outside each shop window. There was no sign of the girls. She noticed the woman with the rack of blouses. She had a packet of some sort in her hand and was extracting what looked like a Mopani worm from within it.

"Mopani worms?" asked Mma Ramotswe. The woman turned round and looked at her. "Yes." She offered the bag to Mma Ramotswe, who helped herself to one of the dried tree worms and popped it into her mouth. It was a delicacy she simply could not resist.

"You must see everything that goes on, Mma," she said, as she swallowed the worm. "Standing here like this."

The woman laughed. "I see everybody. Everybody."

"Did you see two girls come out of the Book Centre?" asked Mma Ramotswe. "One Indian girl and one African girl. The Indian one about so high?"