"He was capable of it," agreed the mechanic, "but he couldn't have done
it that time you tripped him into the mud puddle. This silencer wasn't
built then."

"No, you're right," assented Tom. "Then he must have been around since,
doing some of his tricky work!"

"I don't see how that could have been," said Jackson slowly. "We've
kept a very careful watch, and your shop has been specially guarded."

"I know it has," said Tom. "There couldn't much get past Koku; but some
one seems to have done it, or else how could that filing have been
done?"

Jackson shook his head. The problem was too much for him. He looked
carefully at the exploded and broken silencer, and Tom, too, gave it a
critical eye. There was no doubt but that it had been filed in several
places to weaken the structure of the metal.

"When did you last see that it was in perfect condition?" asked Jackson.

Tom named a certain date.

"That was just before Gale called," observed the mechanician. "He
might have known of it."

"I wish I'd known of it at the time," said Tom savagely. "He wouldn't
have gotten away as easily as he did. Well, there's no use standing
here talking about it. Let's get back to civilization and we'll send
back one of the trucks. Luckily I have another silencer I can put on
for the government test. This one will never be of any more use, though
I may be able to save some of the valves and baffle plates."

Slowly they turned from the disabled aeroplane and started to look for
a path that would lead them out of the lonely place. Tom as the first
to strike what seemed to be a cow path, or perhaps what had been a road
into the wood lot in the early days.

As he tramped along it, followed by Jackson, the young inventor
suddenly stopped, as he came to a sandy place, and, stooping over,
looked intently at some queer marks in the soil.

"What is it?" asked the mechanician.

"Looks like the marks of an automobile," said Tom slowly. "And I was
just trying to remember where I'd seen marks like these before."

CHAPTER XXI

THE DESERTED CABIN

For several seconds the young inventor remained bending over the queer
marks in that little sandy path of the lonely field in the midst of the
silent woods. Jackson watched him curiously, and then Tom straightened
up, exclaiming as he did so:

"I have it! Now I know where it was! I saw marks like these the night
Mr. Nestor disappeared. Mr. Damon and I noticed the marks in the dust