ure the engine is all right. Will you go for a
flight with me?"

"I certainly will! I only wish we could find him, though. I'd go with a
better heart."

"Oh! Mr. Nestor?"

"Yes, I can't imagine what has become of him. It is almost as if the
earth had opened and swallowed him. His disappearance is a great
mystery."

"It surely is," agreed Tom. "Can't seem to get any trace of him. But if
we hear another cry for help, when we have to land, you can make up
your mind I'll investigate more quickly than I did at first."

"I agree with you," said Mr. Damon.

It was nearly evening then, and until it was dark enough for his flight
Tom spent the time tuning up the engine and seeing that all was in
readiness for the latest test. He had decided not to go aloft while it
was light enough for curiosity seekers to note the flight.

Tom rather wished Mary Nestor might have a sail with him in his latest
improved silent Air Scout, but the girl was too much occupied at home
and in trying to find some trace of her father.

Tom, his father, and Mr. Damon had helped all they could, but there
were no results. A private detective had been engaged, but he had no
more of a clew than the regular police.

At last it was dark enough for the flight, and Tom and Mr. Damon took
their places in the machine. Once more the propellers were turned
around, and when the compression had been made, and the spark switched
on, around spun the big wooden blades, and the great craft moved over
the grass.

On and on and up and up sailed Tom and Mr. Damon, and as they left
behind them the shops and the Swift homestead, the two passengers were
aware of their almost silent flight. The big aeroplane, the exhaust of
which, ordinarily, would have nearly deafened them, was now as silent
as a bird.

"Silent Sam for Uncle Sam!" cried Tom in delight, as he went on faster.
"I'm sure the government ought to be glad to get this plane for air
scout work. It's a success! A great success!"

"Yes, so it is!" agreed Mr. Damon. "You do well to speak of it so, Tom."

For, modest as the young inventor was, he felt, in justice to himself,
that he must acknowledge the fact that his craft was a success. For it
rose and sailed almost as silently as a bat, and a few hundred feet
away no one, not seeing it, would have believed a big aeroplane was in
motion.

Tom and Mr. Damon flew about twenty miles at a swift pace, and all the
fault Tom had to find was that the machine was