have been here, either before or
after. No, I'll not say that, either. Finding his wallet here doesn't
prove that he was here. It might have been brought here by one of the
spies and dropped. But I'm sure we're on the track of the men who
damaged my airship, as well as those who know something of the mystery
of Mr. Nestor."

"I agree with you," said Jackson. "Of course there's a possibility that
the same peculiar metal you used in your silencer case may have been
used in some other machine shop, and these files may have come from
there, and have been employed in perfectly regular work. But the
chances are--"

"There's only one way to make sure," said Tom. "Let's take the files
with us and see if they fit in the grooves where the break came. We'll
take these back to where we left the Air Scout," and he clinked the
files he held.

"We can just about make it before it gets black dark," returned
Jackson. "But that won't give us any more time to look around here,"
and he indicated the hut.

"I fancy we've seen all there is to see here," said Tom. "Mr. Nestor
isn't here, and whether he was or not is a question. Anyhow, some one
was here who had something to do with him after his disappearance, I'm
positive of that. And I'm sure some one was here who damaged my
airship. Now we'll run down both those clews, find out who owns this
place, who has been using it, and all we can along that line. So, if
you're ready, let's travel."

The two set out to make their way back to where they had left the
stranded airship. It was fast becoming dark, but they could hurry along
with more speed now, as they did not have to stop to look for the marks
of the peculiar automobile tires. They had noticed the path along which
they had traveled, and in half the time they had spent coming they were
back where the Air Scout rested undisturbed in the meadow amid the
trees.

Making sure that, as far as they could tell, no one had visited the
craft since they had left it, Tom and Jackson compared the file marks
on what was left of the broken silencer case with the files they had
found in the hut. They used a small, but powerful electric lamp to aid
them in this examination, as it was too dark to see otherwise, and what
they saw caused the young inventor to exclaim:

"That settles it! These were the files used!"

"That's right!" agreed his assistant. "You've called the turn, Tom. The
next thing to do is to find who connects with the files."