It proved to be a farm wagon, pulled by two tired nags, and headed for home, after a day in the town market.  The driver was asleep on the seat, leaving to the sagacity of his animals the successful navigation of the road.

Perhaps some movement of the horses or else the bright light of the acetylene headlight falling on his face aroused the man, for he sat up as Frank was about passing.

“Hello! is that you, Frank Bird?” he asked, leaning forward to look closer at the rider of the bicycle.

“Sure; just been up to your neighbor’s, Lovejoy’s, with some medicine for his Sue,” returned the boy, recognizing the farmer.

“How is the gal gettin’ on?” called the other, over the canvas top of his seat.

“Fine.  No danger, dad says!” answered Frank.

“That’s good!” he heard the sympathetic neighbor remark, as he moved on.

Five minutes later and Frank once more found himself approaching the Whympers place.  As before, the house was in complete darkness, as if the inmates were long since abed.  Frank knew that the old man kept early hours, seldom sitting up, for he read much during the day, having nothing else to look after.

Then, as was only natural, the eyes of the bicycle boy turned once again with more or less affection toward the quarter where he could just dimly make out the long, squat shed out in the field, in which the precious monoplane was stored.

As he did so Frank uttered an exclamation of surprise.

“Why, there’s a light over by the hangar!” he burst out.  “Now, what under the sun do you suppose that old fool of a Shea can be doing?  Oh, my!  Look at the flame jump up!  Why, as sure as you live I believe the shed’s afire!  And I can see the figure of a man moving about.  This is no accident, but something worse!  And it looks as if the little ‘Bug’ might be going up in smoke in a jiffy unless I can sprawl over the fence here and get on the spot mighty quick!”

CHAPTER V.

A WARM FIVE MINUTES.

“Fire!  Fire!”

So Frank shouted, even as he jumped over the fence, and made a bee line for the center of the big field, where the shed lay in which the precious monoplane was stored.

He had hastily leaned his bicycle against the fence as he made the plunge.  Nor did he cease to let out constant yells while running across the open as fast as his agile legs could carry him.  Twice he tripped over some object and nearly fell, only to recover himself and speed on.

As he ran he kept his eyes upon the low building beyond.  In this manner he plainly saw the stooping figure of a man or boy making off in a roundabout way so as to avoid him.

Frank’s heart was burning with indignation because of this dastardly attempt to ruin the gallant little airship that had so nobly stood all tests and proven itself a splendid piece of workmanship.