Followed by the secret service operative, the doctor made his way along the edge of the hollow. They did not dare to show a light and it was slow work feeling their way forward, inch by inch. When they had reached a point above where the doctor thought the light had been he paused.
"There must be a ventilation shaft somewhere around here," he whispered, his mouth not an inch from Carnes' ear, "and we've got to find it. It would never do to try the door; if any of them are still here it is sure to be guarded. You go up the hill for five yards and I'll go down. Quarter back and forth on a two hundred yard front and work carefully. Don't fall in, whatever you do. We'll return to this point every time we pass it and report."
The operative nodded and walked a few yards up the hill and made his way slowly forward. He went a hundred yards as nearly as he could judge and then stepped five yards further up the hill and made his way back. As he passed the starting point he approached and Dr. Bird's figure rose up.
"Any luck?" he whispered.
Dr. Bird shook his head.
"Well try further," he said. "I think it is probably beyond us, so suppose you go fifteen yards up and quarter the same as before."
arnes nodded and stole silently away. Fifteen yards up the hill he went and then paused. He stood on the crest of the hill and before him was a steep, almost precipitous slope. He made his way along the edge for a few yards and then paused. Faintly he could detect a murmur of voices. Inch by inch he crept forward, going over the ground under foot. He paused and listened intently and decided that the sound must come from the slope beneath him. A glance at his watch told him that he had spent ten minutes on this trip and he made his way back to the meeting place.
Dr. Bird was waiting for him, and in a low whisper Carnes reported his discovery. The doctor went back with him and together they renewed the search. The slope of the hill was almost sheer and Carnes looked dubiously over the edge.