Tom stopped suddenly. His voice which had been raised to overcome the noise of even the muffled motor, sounded unnaturally loud, and no wonder, for the engine had ceased working! "What's the matter?" gasped Ned. "I don't know--a breakdown of some kind." "Can you get it going again?" "I'm going to try." Tom was manipulating various levers, but with no effect. The aeroplane was shooting downward with frightful rapidity. "No use!" exclaimed the young inventor. "Something has broken." "But we're falling, Tom!" "I know it. We've done it before. I'm going to volplane to earth." This, it may be explained, is gliding downward from a height with the engine shut off. Aeroplanists often do it, and Tom was no novice at the art. They shot downward with less speed now, for the young inventor had thrown up his headplanes to act as a sort of brake. Then, a little later they made a good landing in a field near a small house, in a rather lonely stretch of country, about ten miles from Shopton, where Tom lived. "Now to see what the trouble is," remarked our hero, as he climbed out of his seat and began looking over the engine. He poked in among the numerous cogs, wheels and levers, and finally uttered an exclamation. "Find it?" asked Ned. "Yes, it's in the magneto. All the platinum bearings and contact surfaces have fused and crystallized. I never saw such poor platinum as I've been getting lately, and I pay the highest prices for it, too. The trouble is that the supply of platinum is giving out, and they'll have to find a substitute I guess." "Can't we go home in her?" asked Ned. "I'm afraid not. I've got to put in new platinum bearings and contacts before she'll spark. I only wish I could get hold of some of the better kind of metal." The magneto of an aeroplane performs a service similar to one in an automobile. It provides the spark that explodes the charge of gas in the cylinders, and platinum is a metal, more valuable now than gold, much used in the delicate parts of the magneto. "Well, I guess it's walk for ours," said Ned ruefully. "I'm afraid so," went on Tom. "If I only had some platinum, I could--" "Perhaps I could be of service to you," suddenly spoke a voice behind them, and turning, the youths saw a tall, bearded man, who had evidently come from the lonely house. "Did I hear you say you needed some platinum?" he asked. He spoke with a foreign accent, and Tom at once put him down for a Russian. "Yes, I need some for my magneto," began the young inventor. "If you will kindly step up to my house, perhaps I can give you what you want," went on the man. "My name is Ivan Petrofsky, and I have only lately come to live here." "I'm Tom Swift, of Shopton, and this is my chum, Ned Newton," replied the young inventor, completing the introductions. He was wondering why the man, who seemed a cultured gentleman, should live in such a lonely place, and he was wondering too how he happened to have some platinum.