ussion.

Discovery of the plane had altered their original plans to fly over
the secret radio station. They had decided not to advertise their
presence as, if Frank was correct in his surmise that the other plane
had been watching them, their return would create suspicion and put
the mysterious strangers on guard against them.

"They may be on a perfectly legitimate enterprise, whoever they are,"
Jack said, as all three took seats on the skidway.

"And we may be fools for butting in where we have no business to be,"
said Bob. "That your idea?"

"Yes."

"But look here," said Frank. "I have the feeling that there's
something about all this business that isn't open and aboveboard. I,
for one, vote that we do our best to find out what is going on."

Jack sat silent for several moments.

"That isn't what concerns me at the present moment, after all," he
said. "Whether these people with their strange plane and their secret
radio are on legitimate business or not, doesn't interest me so much.
What puzzles me--and I reckon it puzzles the rest of you, too--is the
design of that plane."

The others nodded vigorously.

"What a tiny thing," was Frank's comment.

"I was busy and couldn't see much," supplemented Bob. "But what
impressed me was her short hood. Why, she looked as if she had no
engine at all."

"That's right," agreed Frank. "I never saw a plane like it. And I
can't recall any designs of that nature, either. It must be a
foreign-built plane, one of those little one-man things the Germans
and French have been building."

Jack shook his head, puzzled.

"There's something strange about it," he said, "a little thing like
that, with practically no engine space. Another thing that you fellows
want to remember, too, is that probably it has been flying about here
for some time, yet we have never heard it. Now, down here the sound of
most planes would travel far, in this quiet and secluded place, where
there are no competing noises."

"Why do you say it has been flying about here for some time?" asked
Bob.

"Well, the familiarity with which the aviator landed shows he's been
at Starfish Cove before. Evidently, after landing he struck inland to
that secret radio station, because we saw no sign of him."

"We haven't been up in the air for three weeks," said Frank. "That
plane might easily have come and gone in that time without our seeing
it. But, surely, as Jack says, we would have heard it at some time or
o