A queer change had come over the prisoner at the sight of Mr. Whitford.  No longer was Shafton surly and blustering.  Instead he seemed to slink down in his chair, bound as he was, as if trying to get out of sight.

“Why did you play double?” demanded the government agent, striding over to him.

“I—­I—­don’t hit me!” whined Shafton.

“Hit you!  I’m not going to hit you!” exclaimed Mr. Whitford, “but I’m going to search you, and then I’m going to wire for one of my men to take you in custody.”

“I—­I didn’t do anything!”

“You didn’t; eh?  Well, we’ll see what the courts think of giving wrong information to Uncle Sam with the intent to aid criminals.  Let’s see what he’s got in his pockets.”

The spy did not have much, but at a sight of one piece of paper Mr. Whitford uttered a cry of surprise.

“Ha!  This is worth something!” he exclaimed.  “It may be stale news, and it may be something for the future, but it’s worth trying.  I wonder I didn’t think of that before.”

“What is it?” asked Tom.

For answer the custom officer held out a scrap of paper on which was written one word.

St. Regis.

“What does it mean,” asked Ned, who, with Mr. Damon, had entered the motor room, and stood curiously regarding the scene.

“Bless my napkin ring!” said the odd man.  “That’s the name of a hotel.  Do you suppose the smugglers are stopping there?”

“Hardly,” replied Mr. Whitford with a smile.  “But St. Regis is the name of an Indian reservation in the upper part of New York state, right on the border, and in the corner where the St. Lawrence and the imaginary dividing line between New York and Canada join.  I begin to see things now.  The smugglers have been flying over the Indian Reservation, and that’s why they have escaped us so far.  We never thought of that spot.  Tom, I believe we’re on the right track at last!  Shafton was probably given this to inform him where the next trick would be turned, so he could get us as far away as possible, or, maybe prevent us leaving at all.”

An involuntary start on the part of the prisoner seemed to confirm this, but he kept silent.

“Of course,” went on Mr. Whitford, “they may have already flown over the St. Regis reservation, and this may be an old tip, but it’s worth following up.”

“Why don’t you ask him?” Tom wanted to know, as he nodded toward Shafton.

“He wouldn’t tell the truth.  I’ll put him where he can’t get away to warn his confederates, and then we’ll go to the reservation.  And to think that my man trusted him!”

Mr. Whitford was soon in communication with his headquarters by means of the wireless apparatus on Tom’s airship, and a little later two custom officers arrived, with an extra horse on which they were to take their prisoner back.

“And now we’ll try our luck once more,” said Mr. Whitford as his men left with Shafton securely bound.  “Can you make the reservation in good time, Tom?  It’s quite a distance,” and he pointed it out on the map.