“You’ll have to sleep somewhere else, Big Foot,” spoke the agent with a laugh.  “Koku, put him down under one of the trees over there.  He can finish his nap in the open, it’s warm.”

The Indian only protested sleepily, as the giant carried him off the ship, and soon Big Foot was snoring under the trees.

“He’s a queer chap,” the custom officer said.  “Sometimes I think he’s a little off in his head.  But he’s good natured.”

Once more they resumed their watching.  It was growing more and more wearisome, and Tom was getting sleepy, in spite of himself.

Suddenly the silence of the night was broken by a distant humming and throbbing sound.

“Hark!” cried Ned.

They all listened intently.

“That’s an airship, sure enough!” cried Tom.

He sprang to the lever that moved the lantern, which had been shut off temporarily.  An instant later a beam of light cut the darkness.  The throbbing sounded nearer.

“There they are!” cried Ned, pointing from a window toward the sky.  A moment later, right into the glare of the light, there shot a powerful biplane.

“After ’em, Tom!” shouted Mr. Whitford.

Like a bird the Falcon shot upward in pursuit noiselessly and resistlessly, the beam of the great searchlight playing on the other craft, which dodged to one side in an endeavor to escape.

“On the trail at last!” cried Tom, as he shoved over the accelerator lever, sending his airship forward on an upward slant, right at the stern of the smugglers’ biplane.

CHAPTER XIX

IN DIRE PERIL

Upward shot the Falcon.  With every revolution of her big propellers she came nearer and nearer to the fleeing craft of the supposed smugglers who were using every endeavor to escape.

“Do you think you can catch them, Tom?” asked Mr. Whitford as he stood at the side of our hero in the pilot house, and looked upward and forward to where, bathed in the light of the great search-lantern, the rival craft was beating the air.

“I’m sure we can—­unless something happens.”

“Bless my overshoes!  What can happen?” asked Mr. Damon, who, after finding that everything in the motor room was running smoothly, had come forward.  Ned was attending to the searchlight.  “What can happen, Tom?”

“Almost anything, from a broken shaft to a short-circuited motor.  Only, I hope nothing does occur to prevent us from catching them.”

“You don’t mean to say that you’re actually going to try to catch them, do you, Tom?” asked the custom officer, “I thought if we could trail them to the place where they have been delivering the goods, before they shipped them to Shopton we’d be doing well.  But I never thought of catching them in mid-air.”

“I’m going to try it,” declared the young inventor.  “I’ve got a grappling anchor on board,” he went on, “attached to a meter and windlass.  If I can catch that anchor in any part of their ship I can bring them to a stop, just as a fisherman lands a trout.  Only I’ve got to get close enough to make a cast, and I want to be above them when I do it.”