‘As do I,’ said Mma Ramotswe. ‘It has no caffeine and therefore you can drink it even when you are about to go to sleep. And it is very good for the skin, I’m told.’

‘Where’s the proof?’ muttered Mma Makutsi. But this question, barbed as it was, was ignored by Mma Ramotswe, who now looked expectantly at Mma Sheba.

‘We have only met once before,’ said Mma Sheba. ‘Do you remember? It was at that lunch in the President Hotel some years ago – the Gaborone Professional Ladies’ Lunch. Remember? We sat next to one another.’

Mma Ramotswe now recalled. ‘Of course! I knew we had met somewhere, but I couldn’t put my finger on it.’

Remembering the occasion, Mma Ramotswe felt a flush of ancient, rekindled embarrassment. The lunch had been an ordeal from start to finish. She had gone at the invitation of one of her clients, an accountant, who had thought it would be interesting for a group that consisted largely of lawyers, doctors and accountants to have a businesswoman from an entirely different field. This friend had been solicitous but had been unable to sit next to her guest at the table as the club’s policy was to break up friends and mix people together. As a result, Mma Ramotswe had found herself seated next to Mma Sheba on one side, and a surgeon on the other. The surgeon was newly qualified but very conscious of her position. She had spoken to Mma Ramotswe politely at first, and then had asked her where she had done her training.

‘But I have not had any training, Mma,’ said Mma Ramotswe. She wondered whether reading Clovis Andersen’s The Principles of Private Detection would count, but decided that it would not. Private detection was largely a matter of common sense, she had concluded.

The surgeon had shown surprise. ‘No training?’ she asked. ‘So anybody can do what you do?’

Mma Ramotswe weighed her answer. ‘Anybody? Probably not anybody, Mma. Some people might not be very good private detectives because they… well, they might not understand people very well. You have to be able to understand people.’

The surgeon smiled. ‘If that’s all, then it must be very easy. Even my grandmother could be a private detective.’

Mma Ramotswe did not say anything and simply looked down at her place setting. A grandmother would make a very good detective, she thought: grandmothers had seen a lot of human nature and could use that knowledge well.

‘Frankly,’ said the surgeon, ‘I’m not sure that private detection counts as a profession. No offence to you, Mma, but if something requires no training, then, well, I wonder whether it should be considered a profession at all.’

Mma Ramotswe kept her eyes fixed on her place setting before her. She soon became aware of a reaction from Mma Sheba beside her.