Mr. J.L.B. Matekoni, who overheard this, shook his head. “It’s a sign of maturity to be able to change your mind when you realise that you’re wrong,” he explained. “It’s the same with fixing a car. If you find out that you’re going along the wrong lines, then don’t hesitate to stop and correct yourself. If, for example, you’re changing the oil seal at the back of a gearbox, you might try to save time by doing this without taking the gearbox out. But it’s always quicker to take the gearbox out. If you don’t, you end up taking the floor out and anyway you have to take the top of the gearbox off, and the prop shaft too. So it’s best to stop and admit your mistake before you go any further and damage things.”

Charlie listened to this—it was a long speech for Mr. J.L.B. Matekoni—and then looked away. He wondered if this was a random example seized upon by Mr. J.L.B. Matekoni, or if he knew about that seal he had tried to install in the old rear-wheel-drive Ford. Could he have found out somehow?

There was little work done in the agency that afternoon. Mma Makutsi restored her desk to the way she liked it to be: papers reappeared, pencils were resharpened and arranged in the right fashion, and files were extracted from the cabinet and placed back on the desk for further attention. Mma Ramotswe watched all this with utter satisfaction and, after she had offered to make the tea—an offer which Mma Makutsi politely declined, pointing out that she had not forgotten her role altogether—she asked her assistant if she would care to have the rest of the afternoon off.

“You may have shopping to do, Mma,” said Mma Ramotswe. “You know that you can have the time off whenever you want for things like that.”

Mma Makutsi had clearly been pleased by this, but again declined. There was filing to do, she insisted; it was extraordinary how quickly filing accumulated; one turned one’s back for a few hours and there it was—piled up. Mma Ramotswe thought that this was also true of detection work. “No sooner do you deal with one case,” she said, “than another turns up. There is somebody coming tomorrow morning. I should really be seeing people about that hospital matter, but I am going to have to be here to see this other person. Unless…”

She glanced across the room at Mma Makutsi, who was polishing her spectacles with that threadbare lace handkerchief of hers. You would think, Mma Ramotswe said to herself, that she would buy herself a new handkerchief now that she had the money, but people held on to things they loved; they just did.

Mma Makutsi finished with her polishing and replaced her large round spectacles. She looked straight at Mma Ramotswe. “Unless?”