Mma Ramotswe leaned forward. ‘Yes?’

‘He referred to his aunt as his mother. He said, “I must show this to my mother.” I then asked him where his mother was, and he turned round to point at the aunt who was talking to somebody at the other end of the fruit garden. And then he stopped and he seemed dismayed by the slip. He said something like, “I mean my aunt. I mean my aunt.” I made nothing of it, but it struck me as odd.’

Mma Ramotswe was silent.

‘A slip of the tongue, no doubt,’ said Gwithie.

Mma Ramotswe put down her teacup. ‘No doubt,’ she said, while thinking: Of course, of course. Quite suddenly, seated under the tree with her friend, with the air so still and hot, with a fly buzzing about the lip of the milk jug on the tea-tray, with all Botswana yearning for rain, it became clear to her. It had not occurred to her before because there was no reason for her to suspect that there was any other relationship between Mma Molapo and the young man who claimed to be Liso. She had been acting on the assumption that he was either her nephew or he was not, and the second of these options had not included the possibility that he was even more closely related to her – that he was a son. But now it seemed so obvious. If Mma Molapo had a son, then she would undoubtedly prefer him to succeed rather than her nephew. So if the nephew proved to be hard to locate, or had vanished altogether, then all she would have to do would be to substitute her son. And if he succeeded, then she could stay exactly where she was; whereas a nephew may well have views of his own as to whether his aunt continued to live on the property. The problem, though, would be that it would not work. There must be many people who had seen the boy over the years – neighbours and people who worked on the farm – and they would know if suddenly a different young man came along and claimed to be the person they had seen over the years. So a substitution was impossible, and that meant that Liso could not be Mma Molapo’s son.

Gwithie said a few words that Mma Ramotswe, sunk in thought, did not catch. Now she repeated them.

‘I’m sorry, Mmapuso,’ said Mma Ramotswe. ‘I was thinking of… something I hadn’t been thinking about… before, that is.’

‘I asked whether you would like to come for a walk with me,’ said Gwithie. ‘A brief walk.’

Mma Ramotswe knew where they would be going.

‘Of course,’ she said. ‘I would like to go with you, Mma. Of course I would.’