They ran into the room and started to conduct a thorough search of all the likely places. When that produced nothing, they used their imaginations. It was Daeng who found the wireless transmitter in the knot atop the mosquito net, just two meters above their nighttime conversations and intimate moments.

“It’s short range,” said Daeng. “He’d have to be within fifty meters.”

“The mysterious guest in room four,” said Siri.

They ran down the stairs to the far end of the building, where the door to room 4 was ajar. They went inside. Beside the unmade bed was a radio receiver. The headphones were on the pillow.

“Looks like he doesn’t need them anymore,” said Siri.

“We have to get to the village,” said Daeng.

“It’s almost dark.”

“It’s a tunnel. How much darker could it be?”

So it was that with no plan and no equipment they headed toward the river. Even before they left the guesthouse grounds they bumped into Beer coming toward them.

“Comrade Beer,” said Daeng. “We need a fast boat with a light.”

“Why? What’s happened?” said Beer.

“We’ll tell you on the way.”

The boat they hired was certainly faster than Garu’s. They arrived at the entrance to the Thum Huk tunnel in record time. But the young driver didn’t have the expertise of the old man. He had a strong beam on the front of his boat but he was bemused by all the twists and turns of the cave network. He refused to go at speed because he was afraid. There was talk of ghosts in the tunnel. So by the time they reached the village the moon was on the rise, nestled now in the low clouds, and there was nobody at the dock. A clunky old WW2 foldable launch was tied up there. There was no artificial lamplight.

“Damn, I wish I’d brought the Kalashnikov,” said Siri.

“I suppose we could have planned this a little better,” Daeng agreed. “But we’re here now. Best make the most of it.”

They’d briefed Beer on the journey. They’d told him about the revelations from Kyoko’s professor and the discovery of the listening device. He’d told them how he’d spent a fruitless day at clinics and pharmacies and even made an appointment with the director of the hospital, who had nothing useful to say. Beer seemed embarrassed by his failure but they congratulated him on his thoroughness.