“Why, I am not at liberty to tell,” went on the man.  “I called to see if we could negotiate with you for the sale of it.  Parties whom I represent—­”

At that moment Tom plucked his father by the sleeve.

“Dad,” whispered the youth, “I saw him in Mansburg.  I think he is one of several who have been inquiring in Mr. Merton’s shop about you and your patents.  I wouldn’t have anything to do with him until I found out more about him.”

“Is that so?” asked Mr. Swift quickly.  Then, turning to the stranger, he said:  “My son tells me—­”

But Mr. Swift got no further, for at that moment the stranger caught sight of Tom, whom he had not noticed before.

“Ha!” exclaimed the man.  “I have forgotten something—­an important engagement—­will be back directly—­will see you again, Mr. Swift—­ excuse the trouble I have put you to—­I am in a great hurry,” and before father or son could stop him, had they any desire to, the man turned and walked quickly from the yard.

Mr. Swift stood staring at him, and so did Tom.  Then the inventor asked: 

“Do you know that man?  What about him, Tom?  Why did he leave so hurriedly?”

“I don’t know his name,” replied Tom, “but I am suspicious regarding him, and I think he left because he suddenly recognized me.”  Thereupon he told his father of seeing the man in the post-office, and hearing the talk of the same individual and two companions in the restaurant.

“And so you think they are up to some mischief, Tom?” asked the parent when the son had finished.

“Well, I wouldn’t go quite as far as that, but I think they are interested in your patents, and you ought to know whether you want them to be, or not.”

“I most certainly do not—­especially in the turbine motor.  That is my latest invention, and, I think, will prove very valuable.  But, though I have not mentioned it before, I expect to have trouble with it.  Soon after I perfected it, with the exception of some minor details, I received word from a syndicate of rich men that I was infringing on a motor, the patent of which they controlled.”

“This surprised me for two reasons.  One was because I did not know that any one knew I had invented the motor.  I had kept the matter secret, and I am at a loss to know how it leaked out.  To prevent any further information concerning my plans becoming public, I sent you to Mansburg to-day.  But it seems that the precaution was of little avail.  Another matter of surprise was the information that I was infringing on the patent of some one else.  I had a very careful examination made, and I found that the syndicate of rich men was wrong.  I was not infringing.  In fact, though the motor they have is somewhat like mine, there is one big difference—­theirs does not work, while mine does.  Their patents are worthless.”

“Then what do you think is their object?”

“I think they want to get control of my invention of the turbine motor, Tom.  That is what has been worrying me lately.  I know these men to be unscrupulous, and, with plenty of money, they may make trouble for me.”