“We roused up other neighbors, and they searched all about the grounds, thinking he might have been overcome by a sudden faint.  But we could not find him.  My husband had disappeared—­ mysteriously disappeared!” and the lady broke into sobs.

“Now don’t worry,” said Tom, soothingly, as he put his arms about her as he would have done to his own mother, had she been alive, “We’ll get him back!”

“But how can you?  No one knows where he is.”

“Oh, yes!” said Tom, confidently, “Mr. Damon himself knows where he is, and unless he has gone away voluntarily, I think you will soon hear from him.”

“What do you mean by—­voluntarily?” asked the wife.

“First let me ask you a question,” came from Tom.  “You said you were awakened by a peculiar noise.  What sort of a sound was it?”

“Why, a whirring, throbbing noise, like—­like—­”

She paused for a comparison.

“Like an airship?” asked Tom, with a good deal of eagerness.

“That was it!” cried Mrs. Damon.  “I was trying to think where I had heard the sound before.  It was just like the noise your airship makes, Tom!”

“That settles it!” exclaimed the young inventor.

“Settles what?” asked Ned.

“The manner of Mr. Damon’s disappearance.  He was taken away—­or went away—­in my airship—­the airship that was stolen from my shed last night!”

Mrs. Damon stared at Tom in amazement.

“Why—­why—­how could that be?” she asked.

Quickly Tom told of what had happened at his place.

“I begin to see through it,” he said.  “There is some plot here, and we’ve got to get to the bottom of it.  Mr. Damon either went with these men in the airship willingly, or he was taken away by force.  I’m inclined to think he went of his own accord, or you would have heard some outcry, Mrs. Damon.”

“Well, perhaps so,” she admitted.  “But would he go away in that manner without telling me?”

“He might,” said Tom, willing to test his theory on all sides.  “He might not have wanted you to worry, for you know you dislike him to go up an airships.”

“Yes, I do.  Oh, if I only thought he did go away of his own accord, I could understand it.  He went, if he did, to try and save his fortune.”

“It does look as though he had an appointment with someone, Tom,” suggested Ned.  “His looking at the clock, and then going out, and all that.”

“Yes,” admitted the young inventor, “and now I’m inclined to change my theory a bit.  It may have been some other airship than mine that was used.”

“How so?” asked Ned.

“Because the men who took mine were unprincipled fellows.  Mr. Damon would not have gone away with men who would steal an airship.”

“Not if he knew it,” admitted Ned.  “Well, then, let’s consider two airships—­yours and the other that came to keep the appointment with Mr. Damon.  If the last is true, why should he want to go away in an airship at midnight?  Why couldn’t he take a train, or an auto?”