It came on to rain after midnight, and a mist crept down from the clouds, so that even with the great searchlight flashing its powerful beams, it was difficult to see for any great distance.

“Better give it up, I guess,” suggested Mr. Whitford toward morning, when they had covered many miles, and had turned back toward Logansville.

“All right,” agreed Tom.  “But we’ll try it again to-morrow night.”

He dropped his craft at the anchorage he had selected in the gray dawn of the morning.  All on board were tired and sleepy.  Ned, looking from a window of the cabin, as the Falcon came to a stop, saw something white on the ground.

“I wonder what that is?” he said as he hurried out to pick it up.  It was a large white envelope, addressed to Tom Swift, and the name was in printed characters.

“Somebody who wants to disguise their writing,” remarked Tom, as he tore it open.  A look of surprise came over his face.

“Look here!  Mr. Whitford,” he cried.  “This is the work of the smugglers all right!”

For, staring at Tom, in big printed letters, on a white sheet of paper, was this message: 

“If you know what is good for you, Tom Swift, you had better clear out.  If you don’t your airship will burned, and you may get hurt.  We’ll burn you in mid-air.  Beware and quit.  You can’t catch us.”

“The committee of three.”

“Ha!  Warned away!” cried Tom.  “Well, it will take more than this to make me give up!” and he crumpled the anonymous warning in his hand.

CHAPTER XIII

KOKU SAVES THE LIGHT

“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.