"We found a fuse on the first sub-level near the shaft, but of course that doesn't prove anything. It may have been dropped there by any one of fifty different men."
The superintendent's face was stern as he pondered over the matter that was disturbing them all.
"Rush, I want you boys to devote your time, during the next few days, to working on this case. I know of no one else better qualified to do it. If you can't get to the bottom of the mystery, I know of no one who can. In the meantime I shall be pursuing some investigations of my own."
"Very well, sir; do you wish us to drop our work?"
"As a matter of fact, yes; but you need not appear to have done so. Pretend to make your rounds, but devote your time to running down this mystery. The officials will be back here within the next few days. I want this affair cleared up before they get here, so work fast. You have my authority to go to any length necessary to solve the mystery and to discover the guilty ones. Now, show me what you can do."
"It is a pretty big contract you have given us, sir, but we will do the best we can. We have personal reasons for wanting to succeed, as you can understand."
The boys bade the superintendent good night and went to their boarding place. The following morning found Rush suffering from a severe cold. He could barely speak, but he went to the mine, nevertheless. The cage was not yet ready for use, but the superintendent had had the ore skips rigged to carry men down, which was done at greatly reduced speed, but at the usual time the mine was in full operation.
All that day the two boys tramped about the mine, part of the time in company and at other times pursuing their investigations separately. They talked with the men, working in various subtle ways to obtain hints that might start them in the right direction.
Night came, but when they compared notes they found that they had made no progress.
"I would go back to-night," said Steve thoughtfully, "but to do so would attract attention. They know we do not work at night and someone might become suspicious."
The next day was a repetition of the previous one so far as results were concerned. Not a clue did either boy find. This went on for three days, during which time they had not seen Mr. Penton. He was giving his two track inspectors a clear field, unhampered by any directions from him, and this put them on their mettle, perhaps more keenly than would otherwise have been the case.