Slowly the airship arose, almost too slowly to suit those on board who anxiously watched the oncoming officers. The latter had drawn their short swords, and at the sight of them Mr. Damon cried out:

"Bless my football! If they jab them into the gas bag, Tom, we're done for!"

"They won't get the chance," answered the young inventor, and he spoke truly, for a moment later, as the big propellers took hold of the air, the Falcon went up with a rush, and was far beyond the reach of the men. In a rage the spy shook his fist at the fast receding craft, and one of the policemen drew his revolver.

"They're going to fire!" cried Ned.

"They can't do much damage," answered Tom coolly. "A bullet hole in the bag is easily repaired, and anywhere else it won't amount to anything."

The officer was aiming his revolver at the airship, now high above his head, but with a quick motion the spy pulled down his companion's arm, and they seemed to be disputing among themselves.

"I wonder what that means?" mused Mr. Damon.

"Probably they didn't want to risk getting into trouble," replied the Russian. "There are strict laws in France about using firearms, and as yet we are accused of no crime. We are only suspected, and I suppose the spy didn't want to get into trouble. He is on foreign ground, and there might be international complications."

"Then you really think he was a spy?" asked Tom.

"No doubt of it, and I'm afraid this is only the beginning of our trouble."

"In what way?"

"Well, of course word will be sent on ahead about us, and every where we go they'll be on the watch for us. They have our movements pretty well covered."

"We won't make a descent until we get to Siberia," said Tom, "and I guess there it will be so lonesome that we won't be troubled much."

"Perhaps," admitted the Russian, "but we will have to be on our guard. Of course keeping up in the air will be an advantage but they may--"

He stopped suddenly and shrugged his shoulders.

"What were you going to say?" inquired Ned.

"Oh, it's just something that might happen, but it's too remote a possibility to work about. We're leaving those fellows nicely behind," he added quickly, as though anxious to change the subject

"Yes, at this rate we'll soon be out of France," observed Tom, as he speeded the ship along still more. The young inventor wondered what Mr. Petrofsky had been going to say, but soon after this, some of the repaired machinery in the motor room needed adjusting, and the young inventor was kept so busy that the matter passed from his mind.

The dynamo and magneto were doing much more efficient work since Tom had put the new platinum in, and the Falcon was making better time than ever before. They were flying at a moderate height, and could see wondering men, women and children rush out from their houses, to gaze aloft at the strange sight. Paris was now far behind, and that night they were approaching the borders of Prussia, as Mn Petrofsky informed them, for he knew every part of Europe.

The route, as laid down by Tom and the Russian, would send the airship skirting the southern coast of the Baltic sea, then north-west, to pass to one side of St. Petersburg, and then, after getting far enough to the north, so as to avoid the big cities, they would head due east for Siberia.

"In that way I think we'll avoid any danger from the Russian police," remarked the exile.

For the next few days they flew steadily on at no remarkable speed, as the extra effort used more gasolene than Tom cared to expend in the motor. He realized that he would need all he had, and he did not want to have to buy any more until he was homeward bound, for the purchase of it would lead to questions, and might cause their detention.

Mr. Damon gave his friends good meals and they enjoyed their trip very much, though naturally there was some anxiety about whether it would have a successful conclusion.

"Well, if we don't find the platinum mine we'll rescue your brother, if there's a possible chance!" exclaimed Tom one day, as he sat in the pilot house with the exile. "Jove! it will be great to drop down, pick him up, and fly away with him before those Cossacks, or whoever has him, know what's up."

"I'm afraid we can't make such a sensational rescue as that," replied Mr. Petrofsky. "We'll have to go at it diplomatically. That's the only way to get an exile out of Siberia. We must get word to him somehow, after we locate him, that we are waiting to help him, and then we can plan for his escape. Poor Peter! I do hope we can find him, for if he is in the salt or sulphur mines it is a living death!" and he shuddered at the memory of his own exile.

"How do you expect to get definite information as to where he might be?" asked Tom.

"I think the only thing to do is to get in touch with some of the revolutionists," answered the Russian. "They have ways and means of finding out even state secrets. I think our best plan will be to land near some small town, when we get to the edge of Siberia. If we can conceal the airship, so much the better. Then I can disguise myself and go to the village."

"Will it be safe?" inquired the young inventor.

"I'll have to take that chance. It's the only way, as I am the only one in our party who can speak Russian."

"That's right," admitted Tom with a laugh. "I'm afraid I could never master that tongue. It's as hard as Chinese."

"Not quite," replied his friend, "but it is not an easy language for an American."

They talked at some length, and then Tom noticing, by one of the automatic gages on the wall of the pilot house, that some of the machinery needed attention, went to attend to it.

He was rather surprised, on emerging from the motor compartment, to see Mr. Damon standing on the open after deck of the Falcon gazing earnestly toward the rear.

"Star-gazing in the day time?" asked Tom with a laugh.

"Bless my individuality!" exclaimed the odd man. "How you startled me, Tom! No, I'm not looking at stars, but I've been noticing a black speck in the sky for some time, and I was wondering whether it was my eyesight, or whether it really is something."

"Where is it?"

"Straight to the rear," answered Mr. Damon, "and it seems to be about a mile up. It's been hanging in the same place this ten minutes."

"Oh, I see," spoke Tom, when the speck had been pointed out to him. "It's there all right, but I guess it's a bird, an eagle perhaps. Wait, I'll get a glass and we'll take a look."

As he was taking the telescope down from its rack in the pilot house, Mr. Petrofsky saw him.

"What's up?" asked the Russian, and the youth told him.

"Must be a pretty big bird to be seen at such a distance as it is," remarked Tom.

"Maybe it isn't a bird," suggested Ivan Petrofsky. "I'll take a look myself," and, showing something of alarm in his manner, he followed Tom to where Mr. Damon awaited them. Ned also came out on deck.

Quickly adjusting the glass, Tom focused it on the black speck. It seemed to have grown larger. Me peered at it steadily for several seconds.

"Is it a bird?" asked Mr. Damon.

"Jove! It's another airship--a big biplane!" cried Tom, "and there seems to be three men in her."

"An aeroplane!" gasped Ned.

"Bless my deflecting rudder!" cried Mr. Damon. "An airship in this out-of-the-way place?" for they were flying over a desolate country.

"And they're coming right after us," added Tom, as he continued to gaze.

"I thought so," was the quiet comment of Mr. Petrofsky. "That is what I started to say a few days ago," he went on, "when I stopped, as I hardly believed it possible. I thought they might possibly send an aeroplane after us, as both the French and Russian armies have a number of fast ones. So they are pursuing us. I'm afraid my presence will bring you no end of trouble."

"Let it come!" cried Tom. "If they can catch up to us they've got a good machine. Come on, Ned, let's speed her up, and make them take more of our star dust."

"Wait a minute," advised the Russian, as he took the telescope from Tom, and viewed the ever-increasing speck behind them. "Are you sure of the speed of this craft?" he asked a moment later.

"I never saw the one yet I couldn't pull away from, even after giving them a start," answered the young inventor proudly. "That is all but my little sky racer. I could let them get within speaking distance, and then pull out like the Congressional Limited passing a slow freight."

"Then wait a few minutes," suggested Mr. Petrofsky. "That is an aeroplane all right, but I can't make out from what country. I'd like a better view, and if it's safe we can come closer."

"Oh, it's safe enough," declared Tom. "I'll get things in shape for a quick move," and he hurried back to the machine room, while the others took turns looking at the on-coming aeroplane. And it was coming on rapidly, showing that it had tremendous power, for it was a very large one, carrying three men.

"How do you suppose they got on our track?" asked Ned.

"Oh, we must have been reported from time to time, as we flew over cities or towns," replied Mr. Petrofsky. "You know we're rather large, and can be seen from a good distance. Then too, the whole Russian secret police force is at the service of our enemies."

"But we're not over Russia yet," said Mr. Damon.

Ivan Petrofsky took the telescope and peered down toward the earth. They were not a great way above it, and at that moment they were passing a small village.

"Can you tell where we are?" asked the odd man.

"We are just over the border of the land of the Czar," was the quiet answer. "The imperial flag is flying from a staff in front of one of the buildings down there. We are over Russia."

"And here comes that airship," called Ned suddenly.

They gazed back with alarm, and saw that it was indeed so. The big aeroplane had come on wonderfully fast in the last few minutes.

"Tom! Tom!" cried his chum. "Better get ready to make a sprint."

"I'm all ready," calmly answered our hero. "Shall I go now?"

"If you can give us a few seconds longer I may be able to tell who is after us," remarked Mr. Petrofsky, turning his telescope on the craft behind them.

"I can let them get almost up to us, and get away," replied Tom.

The Russian did not answer. He was gazing earnestly at the approaching aeroplane. A moment later he took the glass down from his eye.

"It's our spy again," he said. "There are two others with him. That is one of the aeroplanes owned by the secret police. They are stationed all over Europe, ready for instant service, and they're on our trail."

The pursuing craft was so near that the occupants could easily be made out with the naked eye, but it needed the glass to distinguish their features, and Mr. Petrofsky had done this.

"Shall I speed up?" cried Tom.

"Yes, get away as fast as you can!" shouted the Russian. "No telling what they may do," and then, with a hum and a roar the motor of the Falcon increased its speed, and the big airship shot ahead.