“It is strange, though,” Tsukuru said. “If having six fingers is a dominant trait, then why don’t we see more people with them?”

The stationmaster inclined his head. “Don’t know. That kind of complicated stuff is beyond me.”

Sakamoto, who’d eaten lunch with them, opened his mouth for the first time. Hesitantly, as if rolling away a massive stone that blocked the mouth of a cave. “I wonder if you wouldn’t mind if I venture an opinion?”

“Of course,” Tsukuru said, taken by surprise. Sakamoto was not the type of young man who voiced his own opinion in front of others. “Go right ahead.”

“People tend to misunderstand the meaning of the word ‘dominant,’ ” Sakamoto said. “Even if a certain tendency is dominant, that doesn’t mean it becomes widespread throughout the population. There are quite a few rare disorders where genetically there is a dominant gene, but these conditions don’t, as a result, become common. Thankfully, in most cases these are checked at a fixed number, and remain rare disorders. Dominant genes are nothing more than one among many elements in tendency distribution. Other elements would include the survival of the fittest, natural selection, and so on. This is personal conjecture, but I think six fingers are too many for human beings. For what the hand has to do, five fingers are all that are necessary, and the most efficient number. So even if having six fingers is a dominant gene, in the real world it only manifests in a tiny minority. In other words, the law of selection trumps the dominant gene.”

After holding forth at such length, Sakamoto stepped back into silence.

“That makes sense,” Tsukuru said. “I get the feeling it’s connected with the process of how the world’s counting systems have mainly standardized, moving from the duodecimal system to the decimal system.”

“Yes, that might have been a response to six and five fingers, digits, now that you mention it,” Sakamoto said.

“So how come you know so much about this?” Tsukuru asked Sakamoto.

“I took a class on genetics in college. I sort of had a personal interest in it.” Sakamoto’s cheeks reddened as he said this.

The stationmaster gave a merry laugh. “So your genetics class came in handy, even after you started work at a railway company. I guess getting an education isn’t something to be sneezed at, is it.”

Tsukuru turned to the stationmaster. “Seems like for a pianist, though, having six fingers could come in pretty handy.”

“Apparently it doesn’t,” the stationmaster replied. “One pianist who has six fingers said the extra ones get in the way. Like Mr. Sakamoto said just now, moving six fingers equally and freely might be a little too much for human beings. Maybe five is just the right number.”

“Is there some advantage to having six fingers?” Tsukuru asked.

“From what I learned,” the stationmaster replied, “during the Middle Ages in Europe, they thought people born with six fingers were magicians or witches, and they were burned at the stake. And in one country during the era of the Crusaders, anybody who had six fingers was killed. Whether these stories are true or not, I don’t know. In Borneo children born with six fingers are automatically treated as shamans. Maybe that isn’t an advantage, however.”

“Shamans?” Tsukuru asked.

“Just in Borneo.”

Lunchtime was over, and so was their conversation. Tsukuru thanked the stationmaster for the lunch, and he and Sakamoto returned to their office.

As Tsukuru was writing some notes on the blueprints, he suddenly recalled the story Haida had told him, years ago, about his father. How the jazz pianist who was staying at the inn deep in the mountains of Oita had, just before he started playing, put a cloth bag on top of the piano. Could there have been, inside the bag, a sixth right and left finger, preserved in formaldehyde inside a jar? For some reason maybe he’d waited until he was an adult to get them amputated, and always carried the jar around with him. And just before he performed he’d put them on top of the piano. Like a talisman.

Of course, this was sheer conjecture. There was no basis for it. And that incident had taken place—if indeed it had actually occurred—over forty years ago. Still, the more Tsukuru thought about it, the more it seemed like this piece of the puzzle fit the lacuna in Haida’s story. Tsukuru sat at his drafting table until evening, pencil in hand, mulling over the idea.

The following day Tsukuru met Sara in Hiroo. They went into a small bistro in a secluded part of the neighborhood—Sara was an expert on secluded, small bars and restaurants all over Tokyo—and before they ate, Tsukuru told her how he had seen his two former friends in Nagoya, and what they had talked about. It wasn’t easy for him to summarize, so it took a while for him to tell her the whole story. Sara listened closely, occasionally stopping him to ask a question.

“So Shiro told the others that when she stayed at your apartment in Tokyo, you drugged her and raped her?”

“That’s what she said.”

“She described it in great detail, very realistically, even though she was so introverted and always tried to avoid talking about sex.”

“That’s what Ao said.”

“And she said you had two faces?” Sara asked.

“She said I had another dark, hidden side, something unhinged and detached from the side of me that everyone knew.”

Sara frowned and thought this over for a while.

“Doesn’t this remind you of something? Didn’t you ever have some special, intimate moment that passed between you and Shiro?”

Tsukuru shook his head. “Never. Not once. I was always conscious of not letting something like that happen.”

“Always conscious?”

“I tried not to view her as someone of the opposite sex. And I avoided being alone with her as much as I could.”

Sara narrowed her eyes and inclined her head for a moment. “Do you think the others in the group were just as careful? In other words, the boys not viewing the girls as members of the opposite sex, and vice versa?”

“I don’t know what the others were thinking, deep down inside. But like I said, it was a kind of unspoken agreement between us that we wouldn’t let male-female relationships be a part of the group. We were pretty insistent about that.”

“But isn’t that unnatural? If boys and girls that age get close to each other, and are together all the time, it’s only natural that they start to get interested in each other sexually.”

“I wanted to have a girlfriend and to go out on dates, just the two of us. And of course I was interested in sex. Just like anybody else. And no one was stopping me from having a girlfriend outside the group. But back then, that group was the most important part of my life. The thought hardly ever occurred to me to go out and be with anyone else.”

“Because you found a wonderful harmony there?”

Tsukuru nodded. “When I was with them, I felt like an indispensable part of the whole. It was a special feeling that I could never get anywhere else.”

“Which is why all of you had to look past any sexual interest,” Sara said. “In order to preserve the harmony the five of you had together. So as not to destroy the perfect circle.”

“Looking back on it now, I can see there was something unnatural about it. But at the time, nothing seemed more natural. We were still in our teens, experiencing everything for the first time. There was no way we could be that objective about our situation.”

“In other words, you were locked up inside the perfection of that circle. Can you see it that way?”

Tsukuru thought about this. “Maybe that’s true, but we were happy to be locked up inside it. And I don’t regret it, even now.”

“Intriguing,” Sara said.

Sara was also quite interested to hear about Aka’s visit with Shiro in Hamamatsu six months before she was murdered.