t it right away."

Anxious to demonstrate that he was right in his theory, Tom hurried
from the library to get the model of which he had spoken. He left the
roll of plans lying on a small table near where his father was seated.

"There, you see, dad," said the young inventor as he re-entered the
library a few minutes later, "when you warp the wing tips in making a
spiral ascent it throws your tail wings out of plumb, and so--"

Tom paused in some amazement, for Mr. Swift was lying back in his
chair, with his eyes closed. The lad started in alarm, laid aside his
model, and sprang to his father's side.

"He's had another of those heart attacks!" gasped Tom. He was just
going to call Mrs. Baggert, when Mr. Swift opened his eyes. He looked
at Tom, and the lad could see that they were bright, and did not show
any signs of illness.

"Well, I declare!" exclaimed the inventor. "I must have dozed off, Tom,
while you were gone. That's what I did. I fell asleep!"

"Oh!" said Tom, much relieved. "I was afraid you were ill again. Now,
in this model, as you will see by the plans, it is necessary--"

He paused, and looked over at the table where he had left the drawings.
They were not there!

"The plans, father!" Tom exclaimed. "The plans I left on the table!
Where are they?"

"I haven't touched them," was the answer. "They were on that table,
where you put them, when I closed my eyes for a little nap. I forgot
all about them. Are you sure they're missing?"

"They're not here!" And Tom gazed wildly about the room. "Where can
they have gone?"

"I wasn't out of my chair," said Mr. Swift, "I ought not to have gone
to sleep, but--"

Tom fairly jumped toward the long library window, the same one from
which he had leaped to pursue Andy Foger. The casement was open, and
Tom noted that the screen was also unhooked, It had been closed when he
went to get the model, he was sure of that.

"Look, dad! See!" he exclaimed, as he picked up from the floor a small
piece of paper.

"What is it, Tom?"

"A sheet on which I did some figuring. It is no good, but it was in
with the plans. It must have dropped out."

"Do you mean that some one has been in here and taken the plans of your
new aeroplane, Tom?" gasped his father.

"That's just what I mean! They sneaked in here while you were dozing,
took the plans, and jumped out of the window with them. On the way this
paper fell out. It's the only clue we have. Stay here, dad. I'm going