t, I am
thinking of making a smaller monoplane than any that have yet been
constructed, and yet one that will carry two persons. The hardest work
will be to make the engine light enough and still have it sufficiently
powerful to make over a hundred miles an hour, if necessary.

"A hundred miles an hour in a small monoplane! It isn't possible!"
cried the secretary.

"I'll make better time than that," said Tom quietly, and with not a
trace of boasting in his tones.

"Then you'll enter the meet?" asked Mr. Gunmore eagerly.

"Well, I'll think about it," promised Tom. "I'll let you know in a few
days. Meanwhile, I'll be thinking out the details for my new craft. I
have been going to build one ever since I got back, after having seen
my Red Cloud crushed in the ice cave. Now I think I had better begin
active work."

"I hope you will soon let me know," resumed the secretary. "I'm going
to put you down as a possible contestant for the ten-thousand-dollar
prize. That can do no harm, and I hope you win it. I trust--"

He paused suddenly, and listened. So did Tom Swift and his father, for
they all distinctly heard stealthy footsteps under the open windows of
the library.

"Some one is out there, listening," said Tom in low tones.

"Perhaps it's Eradicate Sampson," suggested Mr. Swift, referring to the
eccentric colored man who was employed by the inventor and his son to
help around the place. "Very likely it was Eradicate, Tom."

"I don't think so," was the lad's answer. "He went to the village a
while ago, and said he wouldn't be back until late to-night. He had to
get some medicine for his mule, Boomerang, who is sick. No, it wasn't
Eradicate; but some one was under that window, trying to hear what we
said."

As he spoke in guarded tones, Tom went softly to the casement and
looked out. He could observe nothing, as the night was dark, and the
new moon, which had been shining, was now dimmed by clouds.

"See anything?" asked Mr. Gunmore as he advanced to Tom's side.

"No," was the low answer. "I can't hear anything now, either."

"I'll go speak to Mrs. Baggert, the housekeeper," volunteered Mr.
Swift. "Perhaps it was she, or she may know something about it."

He started from the room, and as he went Tom noticed, with something of
a start, that his father appeared older that night than he had ever
looked before. There was a trace of pain on the face of the aged
inventor, and his step was lagging.

"I guess dad