"Don't do that!" cried Mr. Whitford.
"What?" asked Tom, in some surprise.
"Don't destroy that letter. It may give us a clew. Let me have it. I'll put a man at work on that end of this game."
"Bless my checkerboard!" cried Mr. Damon. "This game has so many ends that you don't know where to begin to play it."
The government man smoothed out the crumpled piece of paper, and looked at it carefully, and also gazed at the envelope.
"It's pretty hard to identify plain print, done with a lead pencil," he murmured. "And this didn't came through the mail."
"I wonder how it got here?" mused Ned. "Maybe some of the crowd that was here when we started off dropped it for the smugglers. Maybe the smugglers were in that crowd!"
"Let's take a look outside," suggested Mr. Whitford. "We may be able to pick up a clew there."
Although our friends were tired and sleepy, and hungry as well, they forgot all this in the desire to learn more about the mysterious warning that had come to them during the night. They all went outside, and Ned pointed to where he had picked up the envelope.
"Look all around, and see if you can find anything more," directed the custom agent.
"Footprints won't count," said Tom. "There was a regular circus crowd out here yesterday."
"I'm not looking for footprints," replied Mr. Whitford, "I have an idea--"
"Here's something!" interrupted Mr. Damon. "It looks like a lead weight for a deep-sea fishing line. Bless my reel. No one could do fishing here."
"Let me see that!" exclaimed Mr. Whitford eagerly. Then, as he looked at it, he uttered a cry of delight. "I thought so," he said. "Look at this bit of cord tied to the weight."
"What does that signify?" asked Tom.
"And see this little hole in the envelope, or, rather a place that was a hole, but it's torn away now."
"I'm not much the wiser," confessed Ned, with a puzzled look.
"Why, it's as plain as print," declared the government agent. "This warning letter was dropped from an airship, Tom."
"From an airship?"
"Yes. They sailed right over this place, and let the letter fall, with this lead weight attached, to bring it to earth just where they wanted it to fall."
"Bless my postage stamp!" cried Mr. Damon. "I never heard of such a thing."
"I see it now!" exclaimed Tom. "While we were off over the river, watching for the smugglers, they were turning a trick here, and giving us a warning into the bargain. We should have stayed around here. I wonder if it was Andy's airship that was used?"
"We can easily find that out," said Mr. Whitford. "I have a detective stationed in a house not far from where the Fogers live. Andy came back from Shopton yesterday, just before you arrived here, and I can soon let you know whether he was out last night. I'll take this letter with me, and get right up to my office, though I'm afraid this won't be much of a clew after all. Print isn't like handwriting for evidence."
"And to think they sailed right over this place, and we weren't home," mourned Tom. "It makes me mad!"
But there was no use in regretting what had happened, and, after a hot breakfast in the airship, with Mr. Damon presiding at the electrical stove, they all felt more hopeful. Mr. Whitford left for his office, promising to send word to Tom as to whether or not Andy was abroad in the airship during the night.
"I wonder if that 'Committee of Three' is Andy and these two fellows with him in the airship?" asked Ned.
"Hard telling," responded his chum. "Now for a good sleep. Koku, keep the crowd away while we have a rest," for the giant had indulged in a good rest while the airship was on patrol during the night.
Not so much of a crowd came out as on the first day, and Koku had little trouble in keeping them far enough away so that Tom and the others could get some rest. Koku walked about, brandishing a big club, and looking as fierce as a giant in a fairy tale. It was afternoon when a message came from Mr. Whitford to the effect that Andy's airship was not out the previous night, and that so far no clews had developed from the letter, or from any other source.
"We'll just have to keep our eyes open," wrote Mr. Whitford. "I think perhaps we are altogether wrong about the Fogers, unless they are deeper than I give them credit for. It might be well to let the smugglers think you are frightened, and go away for a day or so, selecting a more secluded spot to remain in. That may cause them to get bolder, and we may catch them unawares."
"That's a good plan. I'll try it," decided Tom. "We'll move to-morrow to a new location."
"Why not to-night?" asked Ned.
"Because it's getting late, and I want to circle about in daylight and pick out a good place. Morning will do all right."
"Then you're not going out to-night?"
"No. Mr. Whitford writes that as goods were smuggled over last night it will hardly be likely that they will repeat the trick to-night. We'll have a little rest."
"Going to mount guard?" asked Ned.
"No, I don't think so. No one will disturb us."
Afterward the young inventor wished that he had kept a better watch that night, for it nearly proved disastrous for him.
It must have been about midnight that Tom was awakened by a movement in the airship.
"Who's that?" he asked suddenly.
"Koku," came the reassuring reply. "Too hot to sleep in my bunk. I go out on deck."
"All right, Koku," and Tom dozed off again.
Suddenly he was awakened by the sound of a terrific scuffle on deck. Up he jumped, rushing toward the door that led from his sleeping cabin.
"What is it! What's the matter!" he cried.
There came the sound of a blow, a cry of pain, and then the report of a gun.
"Bless my cartridge belt!" cried Mr. Damon.
"What's the matter? Who is it? What happened?" yelled Ned, tumbling out of his bunk.
"Something wrong!" answered Tom, as he switched on the electric lights. He was just in time to see Koku wrench a gun from a man who stood near the pedestal, on which the great searchlight was poised. Tossing the weapon aside, Koku caught up his club, and aimed a blow at the man. But the latter nimbly dodged and, a moment later leaped over the rail, followed by the giant.
"Who is he? What did he do?" cried Tom after his big servant. "What happened?"
"Him try to shoot searchlight, but I stop him!" yelled back Koku, as he rushed on in pursuit. With a leap Tom sprang to the switch of his lantern, and sent a flood of light toward where Koku was racing after the intruder.
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