obliged to you, gentlemen," he said, smoothly, "for
coming to my aid. As it is, however, I do not need help. This is a
plane of my own design, I may as well state, for I can see its
surprising lines have aroused your curiosity. I would prefer that you
do not come any closer but that, on the other hand, you would leave me
now. I want to make some minor repairs, and then I shall be able to
fly again."

"Very well, sir," answered Bob composedly, climbing back from the
fusilage to his seat in the pit. "We don't want to annoy you. Good
day."

With that, Frank swung clear, the propeller to which Bob had given a
twist began anew to revolve, the plane taxied in a circle, then rose
and started for the shore.

"We certainly surprised him," chuckled Jack. "He didn't know what to
say to us. In his excitement and his fear of discovery of some secret
or other, he acted in a way to arouse suspicion, not dispel it. Well,
Frank, you win the gold medal. Your hunch about Higginbotham being
untrustworthy certainly seems to have some foundation."

"I'll say so, too," agreed Bob. "But what do you imagine happened to
him?"

Bob sat with the glasses trained backwards to where the little plane
still rode the sea.

"That's easy," answered Jack. "Something went wrong at the secret
radio plant and the continuity of the dash which provides the juice
for the plane's motor was broken. That's the only way I can figure it.
I say. Let's tune up to 1,375 meters, and see whether that continuous
dash is sounding."

"It's not there," Bob announced presently. "Not a sound in the
receivers. Neither does the plane show any signs of motion. Look here.
Suppose that whatever has happened at that fellow's radio plant
cannot be fixed up for a long period, what will Higginbotham do? Ought
we to go away and leave him?"

"Well," said Jack, doubtfully, "it does look heartless. He's four or
five miles from shore. Of course, we might shoot him a continuous dash
from our own radio plant."

"Zowie," shrieked Bob, snatching the receiver from his head, and
twisting the controls at the same time, in order to reduce from the
1,375-meter wave length. "There's his power. No need for us to worry
now. Oh, boy, but wasn't that a blast in the ear?"

Ruefully, he rubbed his tingling ears. Jack was doing the same. Poor
Frank, whose eardrums had been subjected to the same shock, also had
taken a hand from the levers at the same time and snatched off his
headpiece.

"Sh