"Will that answer?" asked Mr. Petrofsky, when they had reached his house, and he had handed Tom several strips of the precious silverlike metal. "Do? I should say it would! My, but that is the best platinum I've seen in a long while!" exclaimed Tom, who was an expert judge of this metal. "Where did you get it, if I may ask?" "It came from a lost mine in Siberia," was the unexpected answer. "A lost mine?" gasped Tom. "In Siberia?" added Ned. Mr. Petrofsky slowly nodded his head, and smiled, but rather sadly. "A lost mine," he said slowly, "and if it could be found I would be the happiest man on earth for I would then be able to locate and save my brother, who is one of the Czar's exiles," and he seemed shaken by emotion. Tom and Ned stood looking at the bearded man, and then the young inventor glanced at the platinum strips in his hand while a strange and daring thought came to him. CHAPTER II A DARING PROJECT While Tom and his chum are in the house of the Russian, who so strangely produced the platinum just when it was most needed, I am going to take just a little time to tell you something about the hero of this story. Those who have read the previous books of this series need no introduction to him, but in justice to my new readers I must make a little explanation. Tom Swift was an inventor, as was his father before him. But Mr. Swift was getting too old, now, to do much, though he had a pet invention--that of a gyroscope--on which he worked from time to time. Tom lived with his father in the village of Shopton, in New York state. His mother was dead, but a housekeeper, named Mrs. Baggert, looked after the wants of the inventors, young and old. The first book of the series was called "Tom Swift and His Motor-Cycle," and in that I related how Tom bought the machine from a Mr. Wakefield Damon, of Waterford, after the odd gentleman had unintentionally started to climb a tree with it. That disgusted Mr. Damon with motor-cycling, and Tom had lots of fun on the machine, and not a few daring adventures. He and Mr. Damon became firm friends, and the oddity of the gentleman--mainly that of blessing everything he could think of--was no objection in Tom's mind. The young inventor and Ned Newton went on many trips together, Mr. Damon being one of the party. In Shopton lived Andy Foger, a bullying sort of a chap, who acted very meanly toward Tom at times. Another resident of the town was a Mr. Nestor, but Tom was more interested in his daughter Mary than in the head of the household. Add Eradicate Sampson, an eccentric colored man who said he got his name because he "eradicated" dirt, and his mule, Boomerang, and I think you have met the principal characters of these stories.