"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.
