"Name Duncan," he replied in code.
"Will help," was the answer.
"Tell him, 'Quick,'" came the voice of Abdul, close by Duncan's ear.
"Quick," tapped Bruce.
The first faint clicks of a reply came from the steel curtain. Then they ceased.
"He's gone," murmured Duncan.
"Perhaps to help us quickly," answered Abdul. "Listen, burra sahib. I have heard a new noise."
Duncan heard it. He had not noticed it while listening to the clicking sound from the steel barrier. But it attracted his attention now. It was a deep, dull thumping — an ominous, thudding sound that seemed to come from the side walls of their prison.
"Look!" exclaimed Abdul.
Duncan's eyes followed the glare of the flashlight to one side wall of the room. Slowly, inch by inch, the wall was moving toward him. Its speed was sluggish, but constant.