"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 oncoming 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. CHAPTER XVI THE NIHILISTS From the pursuing aircraft came a series of sharp explosions that fairly rattled through the clear air. "Look out for bombs!" yelled Ned. "Bless my safety match!" cried Mr. Damon. "Are they anarchists?" "It's only their motor back-firing," cried Tom. "It's all right, They're done for now, we'll leave them behind."