“But if it’s a tunnel it must lead somewhere,” said Siri. “To enlightenment, if we’re to believe Toshi’s description. So we’d be looking for a tunnel that leads to Nirvana. If he went there on his days off it’s unlikely to be too far away. Easy access.”

“Well, it doesn’t exactly go to Nirvana,” said Beer, “but there’s one very long tunnel that leads to a quaint little village that doesn’t get visited that often. And the name’s right. It’s called Thum Huk.”

“The cave of love,” said Daeng. “How appropriate.”

“There are other more famous caves and tunnels,” said Beer. “But they’re far. Thum Huk you can get to in half a day.”

“How do we go?” Siri asked.

“By river.”

“How about it, wife?” said Siri. “Are you in the mood for an adventure?”

“Ah, you know me, Siri,” said Daeng. “Always up for a wasted day on the trail of someone unimportant.”

“Let’s go, then,” said Siri.

The longboat arrived at the entrance to Thum Huk, which gaped not with wonder but with foreboding. The tunnel mouth seemed to say, “Enter if you dare.”

“How long a walk is it?” Daeng asked the skeletal boatman, who must have been well into a second century.

“Eight kilometers,” he said. “But no need to walk. The river goes right through to the other end. That’s where you’ll find the village of Sawan.”

He reached in front of him and produced an old helmet with a flashlight attachment. He put it on his head and switched it on. It was much too big for him. Only his chin was visible beneath the brim, but that didn’t seem to stop him from navigating. The engine howl became a growl once they were inside. The headlamp was the only illumination and it gave out a dreary halo of light just far enough ahead to know what it was you were about to hit. Yet the boatman did not reduce his speed. In fact he was so self-assured he’d turn his headlamp from time to time to give the glimpse of a stalactite or a tower of crystal. The passengers screamed, “Look ahead!” but Siri was confident the boatman had done the trip so many times he could forfeit his eyesight and still negotiate the caves safely. Some caverns were palatial, the flutter of bats far overhead. Some were mere passageways with sharp turns.