Mary seemed much alarmed, and again begged Tom to be on his guard, which he promised to do.  Had Mary known the warnings uttered by Lieutenant Marbury she might have had more occasion for worry.

“Do you suppose that hammer man of yours came to these woods to meet that Frenchman and talk about you, Tom?” asked his companion, when the two men had strolled out of sight, and the young people were on their way back to the launch.

“Well, it’s possible.  I have been warned that foreign spies are trying to get hold of some of my patents, and also to hamper the government in the use of some others I have sold.  But they’ll have their own troubles to get away with anything.  The works are pretty well guarded, and you forget I have the giant, Koku, who is almost a personal bodyguard.”

“Yes, but he can’t be everywhere at once.  Oh, you will be careful, won’t you, Tom?”

“Yes, Mary, I will,” promised the young inventor.  “But don’t say anything to Ned about what we just saw and heard.”

“Why not?”

“Because he’s been at me to hire a couple of detectives to watch over me, and this would give him another excuse.  Just don’t say anything, and I’ll adopt all the precautions I think are needful.”

“I will on condition that you do that.”

“And I promise I will.”

With that Mary had to be content.  A little later they joined Ned and his friend, and soon they were moving swiftly down the lake in the launch.

“Well, hasn’t it done you good to take a day off?” Ned demanded of his chum, when they were on their homeward way.

“Yes, I think it has,” agreed Tom.

“You swung your thoughts into a new channel, didn’t you?”

“Oh, yes, I found something new to think about,” admitted the young inventor, with a quick look at Mary.

But, though Tom thus passed off lightly the little incident of the day, he gave it serious thought when he was alone.

“Those fellows were certainly talking about me,” he reasoned.  “I wonder what for?  And Feldman left the shop without my knowledge.  I’ll have to look into that.  I wonder if that Frenchy looking chap I saw was the one who tried to pump Eradicate?  Another point to settle.”

The last was easily disposed of, for, on reaching his shops that afternoon, Tom cross-questioned the colored man, and obtained a most accurate description of the odd foreigner.  It tallied in every detail with the man Tom had seen in the woods.

“And now about Feldman,” mused Tom, as he went to the foreman of the shop where the suspected man had been employed.

“Yes, Feldman asked for a day off,” the foreman said in response to Tom’s question.  “He claimed his mother was sick, and he wanted to go to see her.  I knew you wouldn’t object, as we were not rushed in his department.”

“Oh, that’s all right,” said Tom quickly.  “Did he say where his mother lived?”