As Tom passed down the hall on his way to the side door, from which he could more quickly reach the aeroplane shed, he saw his father coming from his room.  
"What's the matter? What is it?" asked Mr. Swift, and alarm showed on his pale face.
 
"It's nothing much, dad," said the youth, as quietly as he could, for he realized that to excite his father might have a bad effect on the invalid¹.
 
"Then why are you in such a hurry? Why have you that revolver? I know there is something wrong, Tom. I am going to help you!"
 
In his father's present weakened state Tom desired this least of all, so he said:
 
"Now, never mind, dad. I thought I heard a noise out in the yard, and I'm not going to take any chances. So I roused Mr. Jackson, and I'm going down to see what it is. Perhaps it may only be Eradicate²'s mule³, Boomerang, kicking around, or it may be Rad himself, or some one after his chickens. Don't worry. Mr. Jackson and I can attend to it. You go back to bed, father."
 
Tom spoke⁴ with such assurance that Mr. Swift believed him, and retired⁵ to his room, just as the engineer, partly dressed, came hurrying out in response to Tom's summons. He had his rifle, and, had the invalid inventor seen that, he surely would have worried more.
 
"Come on!" whispered Tom. "Don't make any noise. I don't want to excite my father."
 
"What was it?" asked the engineer.
 
"I don't know. Burglar alarm went off, that's all I can say until we get to the shed."
 
Together the two left the house softly, and soon were hurrying toward the aeroplane shed.
 
"Look!" exclaimed Mr. Jackson. "Didn't you see a light just then, Tom?"
 
"Where?"
 
"By the side window of the shed?"
 
"No, I didn't notice it! Oh, yes! There it is! Some one is in there! If it's Andy Foger, I'll have him arrested, sure!"
 
"Maybe we can't catch him."
 
"That's so. Andy is a pretty slippery customer. Say, Mr. Jackson, you go around and get Eradicate, and have him bring a club. We can't trust him with a gun. Tell him to get at the back door, and I'll wait for you to join me, and we'll go in the front door. Then we'll have 'em between two fires. They can't get away."
 
"How about the windows?"
 
"They're high up, and hard to open since I put the new catches on them. Whoever got in must have forced the lock of the door. There goes the light again!"
 
As Tom spoke there was seen the faint glimmer⁶ of a light. It moved slowly about the interior of the shed, and with a peculiar⁷ bobbing motion, which indicated that some one was carrying it.
 
"Go for Eradicate, and don't make any more noise than you can help in waking him up," whispered Tom, for they were now close to the shed, and might be heard.
 
Mr. Jackson slipped off in the darkness, and Tom drew nearer to the building that housed his Humming-Bird. There was one window lower than the others, and near it was a box, that Tom remembered having seen that afternoon. He planned to get up on that and look in, before making a raid to capture the intruder.
 
Tom raised himself up to the window. The light had been visible a moment before he placed the box in position, but an instant later it seemed to go out, and the place was in darkness.
 
"I wonder if they've gone away?" thought Tom. "I can't hear any noise."
 
He listened intently. It was dark and silent in the shop. Suddenly the light flashed up brighter than before, and the young inventor caught sight of a man walking around the new aeroplane, examining it carefully. He carried, as Tom could see, a large-sized electric flash-lamp, with a brilliant tungsten filament⁸, which gave a powerful light.
 
As the youth watched, he saw the intruder place the light on a bench, in such a position............