In truth, as the fence was still guarded on top by the powerful current and now was protected from beneath, there was little likelihood that any plotters could get in. Double guards were posted night and day at all entrance gates and not until then did Tom Swift feel secure. He then set to work with redoubled energy to put the finishing touches to his newest patent and felt sure he had solved the one remaining problem—that of making visible all colors on his screen. This he accomplished by filters of glass, something after the manner in which colored moving pictures are taken, but using a process of his own that he had only recently discovered. Though Tom was kept busy putting the finishing touches to his machine, he was not freed from trouble. Every now and then he would get a report from some of his many shops that the place had been entered and things turned upside down, evidently in a search for some of the young inventor’s secrets. “Why don’t they lay off and let me alone?” exclaimed Tom angrily one morning after some particularly annoying damage had been done in his airship shop the night before. “What’s their game, anyhow?” “To make you give up, I guess,” answered Ned. “They can’t get at your talking-picture machine, you’ve got that too well guarded. But to guard the rest of the plant you’d have to keep a full force here day and night, and that’s out of the question with our bank balance as low as it is.” “I realize that, Ned. Yet I’ve got to do something desperate. It may take some money, too.” “Oh, we aren’t down to our last dollar, when it comes to that,” Ned replied. “But it would be ruinous to be paying a night force as well as a day force, particularly when the former would only be used as guards.” “I’m not going to do that,” declared Tom. “It’s time, I think, to put into operation my other scheme—the one I had in mind the night we discovered the bombs.” “What plan is that, Tom?” “It’s an anonymous advertisement in the papers, making certain offers and proposing certain terms to my enemies. Here, I’ll show you what I mean.” Tom thought for a few moments with pencil poised over a pad. Then he wrote rapidly and handed the sheet of paper to Ned. This is what his chum read: RAPID young man, who is being held back in his work by threats and annoying, sneaking night attacks, will pay any reasonable sum just to be let alone so that he may proceed with his inventions. He wants to be swift in completing his work and it can easily be pictured how this talk about making trouble annoys him. A large sum will be paid for freedom from future annoyance. Answer in confidence, QUICK, Box 123 Evening Graphic Office. “Do you intend to insert this advertisement in the _Graphic_?” asked Ned, naming the Shopton evening paper. “That’s what I do. Don’t you think they will understand it even without my name being to it?”