In a short time a squad of police were on guard around Tom’s big plant, while, as the day drew to a close and the hour approached for the test demonstration, the regular workmen searched for anything that might give color to the threat to blow the place up. Just when it seemed that nothing would be found, several of the men, under the leadership of Mr. Jackson, made a startling discovery. They found where the big outside fence had been tunneled under and, working from there, came upon several mines that were planted near important buildings in a manner that would have done credit to a wartime mining party. From the mines buried wires led outside the fence to a little gully. There, beneath a clump of bushes, the ends of the wires lay. All that remained was to connect them to a detonating battery. Then the mines could all be set off at once and the Swift plant surely would be terribly damaged, if not wholly destroyed. “They’re regular fiends!” gasped Ned, when the extent of the vile plot had been laid bare. “Yes, they could easily have blown us up but for that warning,” Tom admitted. “Yet it may all have been a bluff. They might not have gone to extremes. But I dared not take a chance.” “No,” agreed his chum. “Well, what’s the next move?” Tom Swift did not answer immediately. CHAPTER XVII USELESS PLEADINGS TOM SWIFT was profoundly disturbed by the momentous discoveries that had taken place around the Swift Construction Company’s plant. He did not believe it possible, with all his precautions, that so deep and dangerous a plot could have been brought so near to fruition as it had been. “Well?” asked Ned remindingly. “Oh!” and Tom appeared to come out of a disagreeable reverie. “Well, there are several things that must be done, Ned. In the first place we must take newer and better precautions to keep these rascals out.” “That’s plain enough.” “Then the next thing to do is to go ahead with this thing and push it to a conclusion.” “You mean the talking-picture machine?” “That’s it. After that we’ll consider what is next to be done. But you and Mr. Damon had better be getting ready,” and Tom smiled for the first time since Eradicate had given him the threatening note that proved to be such a timely warning. “Ready for what?” Ned wanted to know. “For the performance you are to give for the benefit of Mary, Helen, and the other visitors. They’ll be here soon. It’s getting late.” “Do you mean, in the face of what happened, that you’re going to put on a program of songs and dances?” asked Ned, in astonishment. “Why not?” Tom questioned. “Nothing really happened. There was no blowing up of the plant.” “No, but it came mighty close to it. We don’t know what hour those fellows set for attaching the detonator to the ends of the wires, and then it would have been a skyrocket trip for us.”