“Then is it you?” asked Mma Ramotswe, turning to the younger apprentice.

“I am very clean too, Mma,” he said. “I am always washing my hands. Always. Always.”

“Then it must be me,” said Mma Ramotswe. “I must be the one with greasy hands. It must be me or Mma Makutsi. Maybe we get greasy from opening letters.”

The older apprentice appeared to think about this for a moment. “Maybe,” he said.

“There’s very little point in trying to talk to them,” Mr J.L.B. Matekoni had observed when Mma Ramotswe subsequently told him of this conversation. “There is something missing in their brains. Sometimes I think it is a large part, as big as a carburettor maybe.”

Now Mma Ramotswe heard the sound of voices coming from the garage. Mr J.L.B. Matekoni was saying something to the apprentices, and then there came a mumbling sound as one of the young men answered. Another voice; this time raised; it was Mr J.L.B. Matekoni.

Mma Ramotswe listened. They had done something again, and he was reprimanding them, which was unusual. Mr J.L.B. Matekoni was a mild man, who did not like conflict, and always spoke politely. If he felt it necessary to raise his voice, then it must have been something very annoying indeed.

“Diesel fuel in an ordinary engine,” he said, as he entered her office, wiping his hands on a large piece of lint. “Would you believe it, Mma Ramotswe? That… that silly boy, the younger one, put diesel fuel into the tank of a non-diesel vehicle. Now we have to drain everything out and try to clean the thing up.”

“I’m sorry,” said Mma Ramotswe. “But I am not surprised.” She paused for a moment. “What will happen to them? What will happen when they are working somewhere else-somewhere where there is no longer a kind person like you to watch over them?”