Erlendur watched her staring with interest at Sigurdur Oli and could not suppress a smile.

“It’s about Lake Kleifarvatn,” he said.

Once they had sat down in her living room Sunna told them what she and her colleagues at the Energy Authority believed had happened.

“You remember the big south Iceland earthquake on the seventeenth of June 2000?” she said, and they nodded. “About five seconds afterwards a large earthquake also struck Kleifarvatn, which doubled the natural rate of drainage from it. When the lake started to shrink people at first thought it was because of unusually low precipitation, but it turned out that the water was pouring down through fissures that run across the bed of the lake and have been there for ages. Apparently they opened up in the earthquake. The lake measured ten square kilometres but now it’s only about eight. The water level has fallen by at least four metres.”

“And that’s how you found the skeleton,” Erlendur said.

“We found the bones of a sheep when the surface had dropped by two metres,” Sunna said. “But of course it hadn’t been hit over the head.”

“What do you mean, hit over the head?” Sigurdur Oli said.

She looked at him. She had tried to be inconspicuous when she looked at his hands. Tried to spot a wedding ring.

“I saw a hole in the skull,” she said. “Do you know who it is?”

“No,” Erlendur said. “He would have needed to use a boat, wouldn’t he? To get so far out onto the lake.”

“If you mean could someone have walked to where the skeleton is, the answer’s no. It was at least four metres deep there until quite recently. And if it happened years back, which of course I know nothing about, the water would have been even deeper.”

“So they were on a boat?” Sigurdur Oli said. “Are there boats on that lake?”