That morning, sitting at her desk, a steaming mug of bush tea before her, Mma Ramotswe was alone with her thoughts. It was nine o’clock, which was well into the working morning (which started at seven-thirty), but Mma Makutsi, her assistant, had been instructed to go to the post office on her way to work and would not arrive for a little while yet. Mma Makutsi had been hired as a secretary, but had quickly proved her value and had been promoted to assistant detective. In addition to this, she was Assistant Manager of Tlokweng Road Speedy Motors, a role which she had taken on with conspicuous success when Mr J.L.B. Matekoni had been ill. Mma Ramotswe was lucky to have such an assistant; there were many lazy secretaries in Gaborone, who sat in the security of their jobs tapping at a keyboard from time to time or occasionally picking up the telephone. Most of these lazy secretaries answered the telephone in the same tone of voice, as if the cares of being a secretary were overwhelming and there was nothing that they could possibly do for the caller. Mma Makutsi was quite unlike these; indeed she answered the telephone rather too enthusiastically, and had sometimes scared callers away altogether. But this was a minor fault in one who brought with her the distinction of being the most accomplished graduate of her year from the Botswana Secretarial College, where she had scored ninety-seven per cent in the final examinations.

As Mma Ramotswe sat at her desk, she heard sounds of activity from the garage on the other side of the building. Mr J.L.B. Matekoni was at work with his two apprentices, young men who seemed entirely obsessed with girls and who were always leaving grease marks about the building. Around each light switch, in spite of many exhortations and warnings, there was an area of black discolouration, where the apprentices had placed their dirty fingers. And Mma Ramotswe had even found greasy fingerprints on her telephone receiver and, more irritatingly still, on the door of the stationery cupboard.

“Mr J.L.B. Matekoni provides towels and all that lint for wiping off grease,” she had said to the older apprentice. “They are always there in the washroom. When you have finished working on a car, wash your hands before you touch other things. What is so hard about that?”

“I always do that,” said the apprentice. “It is not fair to talk to me like that, Mma. I am a very clean mechanic.”

“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.