Halting, they waited. In a moment the sound was repeated. Then to their surprise, came an answering whistle from inside Professor Bettenridge’s cabin.
“That must be Webb,” Salt whispered, observing a shadowy form approaching. “The whistle evidently is a signal to make certain the coast is clear.”
As they watched, the hunched figure emerged from the darkness, was silhouetted momentarily in the light which came from the cabin, then disappeared inside.
“I wish we knew what they were talking about in there,” Penny said. “It might clear up some of the mystery.”
“Why not see what we can learn?” proposed Salt. “It’s safe enough.”
Taking care to walk softly, the pair stole back to the cabin. Crouching by the window, they could hear a low murmur of voices inside. At first it was difficult to catch the trend of the conversation, but gradually Professor Bettenridge’s voice grew louder.
“I don’t like it any better than you do,” Salt and Penny heard him say, “but that’s the way it is. If we’re to finish the deal, we’ve got to explode one of Johnson’s mines Thursday night. The question is, can we do it?”
“Depends on the type of mine,” Webb replied gruffly. “How soon can we have it ahead of the test?”
“I’ll insist that he deliver it here at least by afternoon. Will that give you time enough?”
“Sure, it won’t take more than a half hour to fix ’er for the test, providing it can be done. But I ain’t makin’ no promises until I see the mine.”