“Well, seeing as how you have the drop on us, I guess we’ll have to do as you say,” admitted Happy Harry, alias Jim Burke.  “But you can’t prove anything against us.  We haven’t any of Mr. Swift’s property.”

“Well, you know where it is then,” retorted Tom quickly.

Under the restraining influence of the gun the men made no resistance.  While Mr. Sharp covered them, Tom towed their boat toward shore.  Then, while the young inventor held the gun, the balloonist tied the hands and feet of the thieves in a most scientific manner, for what he did not know about ropes and knots was not worth putting into a book.

“Now, I guess they’ll stay quiet for a while,” remarked Mr. Sharp as he surveyed the crestfallen criminals.  “I’ll remain on guard here, Tom, while you go notify the nearest constable and we’ll take them to jail.  We bagged the whole lot as neatly as could be desired.”

“No, you didn’t get all of us!” exclaimed Happy Harry, and there was a savage anger in his tones.

“Keep quiet!” urged Morse.

“No, I’ll not keep quiet!  It’s a shame that we have to take our medicine while that trimmer, Tod Boreck, goes free.  He ought to have been with us, and he would be, only he’s trying to get away with that sparkler!”

“Keep quiet,” again urged Morse.

Tom was all attention.  He had caught the word “sparkler,” and he at once associated it with the occasion he had heard the men use it before.  He felt that he was on the track of solving the mystery connected with his boat.

He looked at the men.  They were the same four who had been involved in the former theft—­Appleson, Featherton, Morse and Burke.  Were there five of them?  He recalled the man who had been caught tampering with his boat—­the man who had tried to bid on the arrow at the auction.  Where was he?

“Boreck didn’t get what he was after,” resumed Happy Harry, “and I’m going to spoil his game for him.  Say, kid,” he went on to Tom, “look in the front part of your boat—­where the gasoline tank is.”

Tom felt his heart beating fast.  At last he felt that he would solve the puzzle.  He opened the forward compartment.  To his disappointment it seemed as usual.  Morse and the others were making a vain effort to silence Happy Harry.

“I don’t see anything here,” said Tom.

“No, because it’s hidden in one of those blocks of wood you use for a brace,” continued the man.  “Which one it is, Boreck didn’t know, so he pulled out two or three, only to be fooled each time.  You must have shifted them, kid, from the way they were when we had the boat.”

“I did,” answered the young inventor, recollecting how he had taken out some of the braces and inserted new ones, then painted the interior of the compartment.  “What is in the braces, anyhow?”

“The sparkler—­a big diamond—­in a hollow place in the wood, kid!” exclaimed Happy Harry, blurting out the words.  “I’m not going to let Tod Boreck get away with it while we stay in jail.”