There was a silence after the inspiring words of the operator, and then it seemed that everyone began to talk at once. The record-breaking shot, the effect of it and the struggle that had taken place in the powder room, together with the flight of von Brunderger and his servant, gave many subjects for excited conversation.

"I've got to get at the bottom of this!" cried Tom, making his way through the press of officials to where the wireless operator stood. "Just repeat that," requested Tom, and they all gave place for him, waiting for the answer.

The operator read the message again.

"Thirty-three miles!" murmured Tom. "That is better than I dared to hope. But what's that about blowing the top off an island?"

"That's what you did, with that explosive shell, Mr. Swift. The operator on the firing-zone ship saw the top fly off when the shell struck. The ship was about half a mile away, and when they heard that shell coming the officers thought it was all up with them. But, instead, it passed over them and demolished the top of the mountain.

"Anybody hurt?" asked Tom, anxiously.

"No, it was an uninhabited island. But you have made the record shot, all right. It went farther than any of the others."

"Then I suppose I ought to be satisfied," remarked Tom, with a smile.

"What was that disturbance, Mr. Swift?" asked the chief ordnance officer, coming forward.

"I don't understand it myself," replied the young inventor. "It appeared that someone went into the ammunition room, and Koku, my giant servant, attacked him."

"As he had a right to do. But who was the intruder?"

"Herr von Brunderger's man."

"Ha! That German officer's! Where is he, he must explain this."

But Herr von Brunderger was not to be found, nor was his man in evidence. They had fled, and when a search was made of their rooms, damaging evidence was found. Before a board of investigating officers Koku told his story, after the gun tests had been declared off for the day, they having been most satisfactory.

The German officer's servant, it appeared, had managed to gain entrance to the ammunition chamber by means of a false key to the outer door. There were two entrances, the other being from the top of the platform where the cannon rested. Koku had seen him about to throw something into one of the ammunition cases, and had grappled with him. There was a fight, and, in spite of the giant's strength, the man had slipped away, leaving part of his garments in the grasp of Koku.

An investigation of some of the powder showed that it had been covered with a chemical that would have made it explode prematurely when placed in the gun. It would probably have wrecked the cannon by blowing out the breech block, and might have done serious damage to life as well as property.

"But what was the object?" asked Ned.

"To destroy Tom's gun," declared Mr. Damon.

"Why should von Brunderger want to do that?"

They found the answer among his papers. He had been a German officer of high rank, but had been dismissed from the secret service of his country for bad conduct. Then, it appeared, he thought of the plan of doing some damage to a foreign country in order to get back in the good graces of his Fatherland.

He forged documents of introduction and authority, and was received with courtesy by the United States officials. In some way he heard of Tom's gun, and that it was likely to be so successful that it would be adopted by the United States government. This he wanted to prevent, and he went to great lengths to accomplish this. It was he, or an agent of his, who forged the letter of invitation to General Waller, and who first tried to spoil Tom's test by doping the powder through Koku.

Later he tried other means, sending a midnight visitor to Tom's house and even going to the length of filing the cables in the storm, so the gun would roll off the warship into the sea. All this was found set down in his papers, for he kept a record of what he had done in order to prove his case to his own government. It was his servant who tried to get near the gun while it was being cast.

That he would be restored to favor had he succeeded, was an open question, though with Germany's friendliness toward the United States it is probable that his acts would have been repudiated. But he was desperate.

Failing in many attempts he resolved on a last one. He sent his servant to the ammunition room to "dope" the powder, hoping that, at the next shot, the gun would be mined. Perhaps he hoped to disable Tom. But the plot failed, and the conspirators escaped. They were never heard of again, probably leaving Panama under assumed names and in disguise.

"Well, that explains the mystery," said Tom to Ned a few days later. "I guess we won't have to worry any more."

"No, and I'm sorry I suspected General Waller."

"Oh, well, he'll never know it, so no harm is done. Oh, but I'm glad this is over. It has gotten on my nerves."

"I should say so," agreed Ned.

"Bless my pillow sham!" cried Mr. Damon. "I think I can get a good night's sleep now. So they have formally accepted your giant cannon, Tom?"

"Yes. The last tests I gave them, showing how easily it could be manipulated, convinced them. It will be one of the official defense guns of the Panama Canal."

"Good! I congratulate you, my boy!" cried the odd man. "And now, bless my postage stamp, let's get back to the United States."

"Before we go," suggested Ned, "let's go take a look at that island from which Tom blew the top. It must be quite a sight--and thirty-three miles away! We can get a launch and go out."

But there was no need. That same day Alec Peterson came to Colon inquiring for Tom. His face showed a new delight.

"Why," cried Tom, "you look as though you had found your opal mine."

"I have!" exclaimed the fortune-hunter. "Or, rather, Tom, I think I have you to thank for finding it for me."

"Me find it?"

"Yes. Did you hear about the top of the island-mountain you blew to pieces?"

"We did, but--"

"That was my island!" exclaimed Mr. Peterson. "The mine was in that mountain, but an earthquake had covered it. I should never have found it but for you. That shot you accidentally fired ripped the mountain apart. My men and I were fortunately at the base of it then, but we sure thought our time had come when that shell struck. It went right over our heads. But it did the business, all right, and opened up the old mine. Tom, your father won't lose his money, we'll all be rich. Oh, that was a lucky shot! I knew it was your cannon that did it."

"I'm glad of it!" answered the young inventor, heartily. "Glad for your sake, Mr. Peterson."

"You must come and see the mine--your mine, Tom, for it never would have been rediscovered had it not been for your giant cannon, that made the longest shot on record, so I'm told."

"We will come, Mr. Peterson, just as soon as I close up matters here."

It did not take Tom long to do this. His type of cannon was formally accepted as a defense for the Panama Canal, and he received a fine contract to allow that type to be used by the government. His powder and projectiles, too, were adopted.

Then, one day, he and Ned, with Koku and Mr. Damon, visited the scene of the great shot. As Mr. Peterson had said, the whole top of the mountain had been blown off by the explosive shell, opening up the old mine. While it was not quite as rich as Mr. Peterson had glowingly painted, still there was a fortune in it, and Mr. Swift got back a substantial sum for his investment.

"And now for the good old U. S. A.!" cried Tom, as they got ready to go back home. "I'm going to take a long rest, and the only thing I'm going to invent for the next six months is a new potato slicer." But whether Tom kept his words can be learned by reading the next volume of this series.

"Bless my hand towel!" cried Mr. Damon. "I think you are entitled to a rest, Tom."

"That's what I say," agreed Ned.

"I'll take care ob him--I'll take care ob Massa Tom," put in Eradicate, as he cast a quick look at Koku. "Giants am all right fo' cannon wuk, but when it comes t' comforts Massa Tom gwine t' 'pend on ole 'Radicate; ain't yo' all, Massa Tom?"

"I guess so, Rad!" exclaimed the young inventor, with a laugh. "Is dinner ready?"

"It suah am, Massa Tom, an' I 'specially made some oh dat fricasseed chicken yo' all does admire so much. Plenty of it, too, Massa Tom."

"That's good, Rad," put in Ned. "For we'll all be hungry after that trip to the island. That sure was a great shot Tom--thirty- three miles!"

"Yes, it went farther than I thought it would," replied Tom. And now, as they are taking a closing meal at Panama, ready to return to the United States, we will take leave of Tom Swift and his friends.