Mma Makutsi clearly thought she was getting somewhere. “So if somebody comes along and says, ‘I am Mma Potokwane’ and she is not the Mma Potokwane we know, then what are we to conclude, Mma?”

Mma Ramotswe shrugged. “We would conclude that this is not the Mma Potokwane we have known for a long time.”

“But would we conclude more than that?”

“I’m not sure.”

“Well, I am, Mma,” said Mma Makutsi forcefully. “I would conclude that the person who says, ‘I am Mma Potokwane’ is a liar. That is what I’d conclude.”

“Unless this person was very confused,” said Mma Ramotswe. “If the person were ill, for example, and not thinking straight. Such a person might claim to be Mma Potokwane but would not necessarily be a liar.”

Mma Makutsi grudgingly accepted that there could be such delusions. “But leaving aside such cases, Mma, what if a person who is not ill says, ‘I am Mma Potokwane’? Such a person would have to be a liar.”

“Maybe…”

“Not maybe, Mma. Definitely.”

Mma Ramotswe looked up at the ceiling. They were sitting in the office when this conversation took place and she felt hot and uncomfortable. The rains had to come soon; there had to be relief from this severe heat that was like a hammer on the land, and the dryness that came with it. She was not sure that she wanted to have a hair-splitting argument with Mma Makutsi, but there were issues here that had to be addressed. If she allowed Mma Makutsi to win every argument, then she would be giving up on a duty that Clovis Andersen identified as one of the real threats to successful and principled detective work. Don’t make any false assumptions, he wrote. Don’t jump to conclusions. Explore every possibility.

“It’s possible,” Mma Ramotswe began, “that these Rosies might not be liars.”

Mma Makutsi was quick to retort. “Two of them must be,” she said, “even if all three aren’t.”

“But what if one—or more—of them thinks that she is Rosie?”

Mma Makutsi scoffed at this. “How could she, Mma. You know who you are; I know who I am. How can you think that you’re somebody you aren’t? It’s impossible.”

“Unless your name is Rosie.”

Mma Makutsi was disconcerted by this answer. “If your name…”

“Rosie is a common enough name, Mma Makutsi. So there might be many Rosies in Gaborone—there probably are, in fact. Just as there are many Graces, I think, and quite a few ladies called Precious too.”

“But even if they are Rosies,” objected Mma Makutsi, “they will know that they are not this Rosie—the one who looked after Mma Susan.”