him to investigate.

So he softly arose to his knees and crept after the shadowy figure.

Cautiously he approached the place where the door belonging to the
storeroom was to be found. As he advanced thus he could occasionally
catch a peculiar clicking sound, which he believed must be made by some
one trying to pick the lock!

The engine of the boat kept up considerable of a racket as it steadily
worked along without the dreaded hitch. Besides, there was always more
or less splashing of water against the sides, as they pushed against the
swift current of the Magdalena. All these things combined to muffle the
clicking sound frequently, yet during little lulls Frank could catch it
again.

The tumult also served to deaden any shuffling he may have made while
creeping toward the lazerette door, and for this Frank was thankful.

It was very gloomy here. A hanging lantern some distance away only
served to accentuate the gloom apparently. Still, by straining his eyes,
Frank believed he could just manage to make out a stooping figure at the
door. Yes, he was certain that it had just moved, and now the peculiar
clicking was much plainer.

When it stopped he remained perfectly motionless, nor did he again
commence his creeping forward progress until it started once more.

Frank no longer had the slightest doubt concerning the cause of that
suspicious clicking. One of the crew was endeavoring to force an
entrance into the locked lazerette, doubtless with the intention of
destroying the valuable aeroplane. He might be in league with the
revolutionists and in this way hoped to prevent the government from
eventually securing possession of the machine which would put the
insurrectos out of the running.

But Frank had conceived another idea. He now believed that his fellow
might have been sent by the crew to destroy the "devil-bird," as they
undoubtedly considered a contraption that could soar through space as
fast as the fleetest condor.

No matter. It was his business to put a sudden stop to the action. And
while doing so he must not be too rough in his dealing with the fellow,
lest the entire crew rise in revolt.

When he had reached a point that allowed of a leap, Frank suddenly
sprang forward. He did not know just what he might be up against and had
even taken from his pocket the splendid new pistol which Colonel Josiah,
himself a world traveler, had insisted upon giving each of his boys
before they started on their tri