"Then you won't take a ride with me to-day. asked the young inventor, of the Russian, as he completed the repairs to the magneto. "I'd like to have you meet my father, and a friend of his, Mr. Damon. Most likely he'll go to Siberia with us, if his wife will let him. I'd like to talk some plans over with you."

"I shall certainly call on you," answered Ivan Petrofsky, "but," he added with a smile, "I think I should prefer to take my first ride in your larger airship--the one that doesn't come down so often."

"Well, perhaps it is a little easier on an amateur," admitted Tom. "If you'll come over to our house at any time I'll take you out in it, or I'll call for you."

"I'll come over in a few days," answered the escaped exile. "Then I'll tell you all I know of the locality where the platinum mine is located, and we can make our plans. In the meanwhile don't say anything about what I have told you."

"Why?" asked Ned quickly.

Mr. Petrofsky approached closer to the lads, and in a low voice said:

"I am not sure about it, but of late I think I have been shadowed. I have seen strange men in the village near here and they have eyed me rather suspiciously. Then, too, I have surprised several men around my house. I live here all alone, you know, and do most of my own work, a woman coming in occasionally to clean. But I don't like these suspicious characters hanging about.

"Who do you think they are?" asked Tom

"I'm almost afraid to think, but from my past experience I think--nay, I fear--they may be spies, or agents of the Russian government"

"Spies!" cried Ned.

"Hush. Not so loud," cautioned Mr. Petrofsky. "They may even now be in hiding, especially since your aeroplane landed so near my house. They may see something suspicious even in that."

"But why should the Russian government set spies on you?" asked Tom in a low voice.

"For two reasons. I am an escaped exile, and I am not a citizen of the United States. Therefore I may be sent back to the sulphur mines. And another reason is that they may think I know the secret of the platinum treasure--the lost mine."

"Say this is getting interesting!" exclaimed Tom. "If we are going to have a brush with some of the spies of the Russian government so much the better. I'm ready for 'em!"

"So am I!" added Ned.

"You don't know them," said Mr. Petrofsky, and he could not repress a shudder. "I hope they are not on my trail, but if they are--" he paused a moment, straightened himself up, and looked like what he was, a strong man-- "if they are let them look out. I'd give my life to save my brother from the awful, living death to which he is consigned!"

"And we're with you!" cried Tom, offering the Russian his hand. "We'll turn the trick yet. Now don't forget to come and see us. Come along, Ned. If I'm going to build an air glider I've got to get busy." And waving farewells to their new friend, the lads took their places in the aeroplane and were soon on their way to Shopton.

"Well, what do you think of it?" asked Ned of his chum, as they sped along at a good elevation, the engine going at half speed to be less noisy and make talking easier.

"Lots. I think we're in for a good time." an exciting one, anyhow, if what he says is true. But what in the world is an air glider, Tom?"

"It's the last word in aeroplanes. You don't need a motor to make it go."

"Don't need a motor?"

"No, the wind does it all. It's a sort of aeroplane, but the motion comes from the wind, acting on different planes, and this is accomplished by shifting weights. In it you can stand still in a fierce gale, if you like."

"How, by tying her fast on the ground?"

"No, hovering in the air. It's all done by getting the proper balance. The harder the wind blows the better the air glider works, and that's why I think it will be just the thing for Siberia. I'm going to get right at work on it, and you'll help me; won't you?"

"I sure will. Say, is platinum worth much?"

"Worth much? I should say it was! It's got gold beat now, and the available supply is very small, and it's getting more scarce. Russia has several mines, and the metal is of good quality. I've used some Russian platinum, but the kind Mr. Petrofsky gave me to-day was better than the best I ever had. If we can only find that lost mine we'll be millionaires all right."

"That's what we thought when we found the city of gold, but the gold wasn't of as fine a grade as we hoped."

"Well, nothing like that can happen in this platinum deal. It sure is rich ore that Mr. Petrofsky and his brother found. Poor fellow! To think of being an exile in that awful country, not knowing where you may be sent next. No wonder Mr. Petrofsky wants to rescue him."

"That's right. Well, here we are. I wonder what your father will say when he hears you're thinking of another expedition, Tom?"

"Oh, he'll want me to go when he hears about the exile."

"And I'm sure my folks will let me go. How about Mr. Damon?"

"I don't believe we can hold him back. It will make a nice party, just you and I, and Mr. Damon and Mr. Petrofsky. That will leave room for the other Russian--if we can rescue him," and with that Tom shut off the engine and glided to earth.

It may well be imagined that Mr. Swift was surprised when his son told him the latest news, but he did not offer any serious objection to the young inventor going to Siberia.

"Only you must be careful," he said. "Those Russian officers are ugly when it comes to trying to take away any of their prisoners. And this air glider--I don't exactly know about that. It's a new machine, and you want to be sure it works before you trust yourself to it."

"I will," promised Tom. "Say, I've got plenty of work ahead of me,--to get my big airship in shape, and build the glider. You'll have to help me, dad."

"I will, son. Now tell me more about this Mr. Petrofsky." Which Tom did.

The days that followed were indeed busy ones for Tom. The young inventor made a model air glider that sailed fairly well, but he knew it would have to work better to be successful, and he bent all his energies in that direction. Meanwhile Mr. Damon had been told of the prospective trip.

"Bless my bank book! Of course I'll go," he said. "But don't say anything about it to my wife--that is, just yet. I'll bring her around to it gradually. She has always wanted a diamond ring set in platinum, and now I can get it for her. I know she'll let me go if I break it to her gently."

It may be mentioned here that many valuable diamonds are now set in platinum instead of gold.

"I want to keep busy," said Mr. Damon, so Tom set him, Ned and Eradicate at the task of getting the big airship in shape for the trip. This air craft has not figured in any of my previous stories, but as it is so nearly like the one that was crushed in the caves of ice, I will not give a description of it here. Those who care to may refer to the book telling of Tom's trip to the caves of ice for a detailed account of the craft.

Sufficient to say that this latest airship, named the Falcon, was the largest Tom had ever built. It contained much room, many comforts, and could sail for several thousand miles without descending, except in case of accident. It was a combined dirigible balloon and aeroplane, and could be used as either, the necessary gas being made on board. It was large enough to enable the air glider to be taken on it in sections.

It was about a week after their first meeting with him, that Ivan Petrofsky paid a visit to the Swift home. He was warmly welcomed by the aged inventor and Mr. Damon, and, closeted in the library of the house, he proceeded to go more into details of his own and his brother's exile to Siberia, and to tell about the supposed location of the lost platinum mine.

"I don't believe we can start for several weeks yet," said Tom, after some discussion. "It will take me that long to make the glider."

"And I, too, need a little time," said the Russian. "I will write to some friends in St. Petersburg and perhaps they can get some information for us, as to where my brother is.

"That will be good," declared Mr. Damon. "Bless my icicle! But the more I think of this trip the better I like it!"

It was arranged that the Russian should call again soon, when the plans would be nearer in shape, and in the meanwhile he must learn all he could from revolutionary friends in Siberia.

It was a week after this, during which Tom, Ned and the others had been very busy, that Tom decided to take a trip to see their Russian friend. They had not heard from him since his visit, and Tom wanted to learn something about the strength of the Siberian winds.

He and Ned went in one of the small airships and soon they were hovering over the grounds surrounding the lonely house where Ivan Petrofsky lived.

"He doesn't seem to be at home," remarked Ned, as they descended and approached the dwelling.

"No, and it looks quite deserted," agreed the young inventor. "Say, all the doors are open, too! He shouldn't go away and leave his house open like that--with the valuable platinum there."

"Maybe he's asleep," suggested Ned.

They knocked on the opened door, but there was no answer. Then they went inside. To their surprise the house was in confusion. Furniture was overturned, tables and chairs were broken, and papers were scattered about the room.

"There's been a fight here!" cried Tom.

"That's right," agreed Ned. "Maybe he's been hurt--maybe burglars came for the platinum!"

"Come on!" cried Tom, making a dash for the stairs. "We'll see if he's here."

The house was small, and it took but a moment to show that Mr. Petrofsky was not there. Upstairs, as below, was the same confusion--the overturned furniture and the papers scattered about.

Tom stooped and picked up a scrap that looked like a piece torn from a letter. On top was a seal--the black seal of Russia--the imperial arms of the Czar!

"Look!" cried Tom, holding out the paper.

"What is it." asked Ned.

"The hand of the Czar!" answered his chum. "It has reached out from Russia, and taken Mr. Petrofsky away!"