Tan insisted on coming and sat beside the sergeant with the air of a battle commander as he drove them out of the compound, switching off the headlights as they reached a dirt track Shan had marked that day. The going was slow, with only a gibbous moon to light their way, and it took nearly a quarter-hour to reach the flat in front of the cave mouth. Shan found a flashlight in the glove box and the sergeant handed Tan the powerful light he carried on his equipment belt.

The collapse of the cavern had started twenty feet inside the entrance, and the base of the sloping pile of shattered rock it had created began several paces inside, leaving the outermost portion of the entry walls still intact and visible to their lights. Even that small section revealed the working of multiple cultures. On each side intricate images of Bon deities had been painted above a row of elongated stick-figure shapes, some carved into the rock and some in faded paint on the surface. Shan made out horses, yaks, and deer among the ancient shapes. An angular image he would not have recognized except for the photos Cao had shown him he knew to be a horned eagle.

Tan aimed his light at each of the more detailed images painted above the more primitive shapes. “Demons,” he observed.

Shan recognized several of the images. “Apchi, Begtse, red Cumara, and Pehar,” he said, pointing to each as he named them. “Protector demons, yes,” he confirmed.

Tan’s light lingered on a flaming sword held in a hand that extended out of the wall of rubble. “Warriors,” he said in an approving tone. “That one died fighting.”

Shan gazed forlornly at the debris. Somewhere deep inside it covered the bodies of the two dead archaeologists.

“That’s not Buddhist,” Tan said. Shan followed his light to a small unobtrusive mark in ochre that was no bigger than his hand. It was the Christian cross Shan had seen in Cao’s photo.

“It was the Valley of the Gods,” Shan said. “I think all gods were welcomed here.” The Jesuit explorer described by Cao had stood in the cave entrance more than three centuries earlier, and had no doubt felt the same excitement that Shan experienced in knowing that devout hands had been at work here for thousands of years. His cross wasn’t there to preempt anything. It was just a greeting from the devout of the West.

Tan silently paced along the images. “Why exactly are we here?” he asked at last.

“You heard the director. They are going to finish the job tomorrow.”