Mma Makutsi bent forward to get a closer view. Then, lifting her head very slowly, she addressed Mma Ramotswe. Her tone was perfectly even. ‘They were copied on the same machine, Mma.’

Mma Ramotswe crossed to her desk and peered over her shoulder.

‘You see, Mma,’ explained Mma Makutsi. ‘Down the side of this leaflet there is that wavy black mark. And down the side of this one here – exactly the same wavy black line. I believe these things are caused by some impurity on the ink cartridge, or on the mirror inside the machine, or something like that.’

Mma Ramotswe saw what she meant. ‘That is amazing, Mma,’ she said. ‘That is detective work of the highest order.’

Mma Makutsi gave a modest shrug. ‘It is knowing what to look for,’ she said. ‘That is all. I’m sure you would have seen the same thing when you started to look for it.’

‘If I started to look for it,’ Mma Ramotswe corrected. ‘I’m not sure that I would have thought of that, Mma.’

‘You would,’ said Mma Makutsi. ‘You have always thought of these things, Mma. So I am sure you would have thought of doing this.’

Mma Ramotswe returned to her desk. ‘What now, Mma?’

‘We go to see our friend, Daisy Manchwe, and we present her with the evidence. That is what we must do, Mma Ramotswe.’

‘And then?’

‘That is for you to decide, Mma,’ said Mma Makutsi. ‘Remember: I am only an associate detective.’ She smiled sweetly. ‘If I were a principal detective, then no doubt I would be able to suggest what we should do. But…’ The smile changed to a look of slight reproach. ‘But I am not that, of course.’

And what about us, boss?

They both gave a start. Mma Ramotswe imagined that she had heard something, a high-pitched, thin voice, rather what one would imagine a bird would sound like if a bird were to talk. But she was not sure. And nor was Mma Makutsi, although she looked down furtively and shifted her feet.

They decided not to go immediately, but to make the trip after lunch. This would enable Mma Makutsi to accompany Mma Ramotswe, having first taken the baby back to the house to be looked after by the nurse. It would also enable Mma Makutsi to attend to the filing that she felt had been badly overlooked. As papers were unearthed, quickly read to assess their content and then placed in carefully separated pending files, Mma Makutsi uttered the occasional tut, tut! accompanied by a shake of the head that was at the same time both approving and disapproving.