Tom Swift, after his arrival home, went on an expedition among a gang of men known as the "Diamond Makers" who were hidden in the Rocky Mountains. He was accompanied by Mr. Barcoe Jenks, one of the castaways of Earthquake Island. They found the diamond makers, and had some surprising adventures, barely escaping with their lives. This did not daunt Tom, however, and he once more started off on an expedition in his airship the Red Cloud to Alaska, amid the caves of ice. He was searching for a valley of gold, and though he and his friends found it, they came to grief. The Fogers, father and son, tried to steal the gold from them, and, failing in that, incited the Eskimos against our friends. There was a battle, but the forces of nature were even more to be dreaded than the terrible savages. The ice cave, in which the Red Cloud was stored, collapsed, crushing the gallant craft, and burying it out of sight forever under thousand of tons of the frozen bergs. After a desperate journey Tom and his friends reached civilization, with a large supply of gold. Tom regretted very much the destruction of the airship, but he at once set to work on another--a monoplane this time, instead of a combined aeroplane and dirigible balloon. This new craft he called the Humming-Bird and it was a "sky racer" of terrific speed. In it, as we have said, Tom brought a specialist to operate on his father, when, because of a broken railroad bridge, the physician could not otherwise have gotten to Shopton. He and Tom traveled through the air at the rate of over one hundred miles an hour. Later, Tom took part in a big race for a ten-thousand-dollar prize, and won, defeating Andy Foger, and a number of well-known "bird-men" who used biplanes and monoplanes of a more or less familiar type. The government became interested in Tom's craft, the Humming-Bird, and, as told in the ninth book of this series, Tom Swift and His Sky Racer, they secured some rights in the invention. And now Tom, who had done nothing for several months following the great race--that is, nothing save to work on his new rifle--Tom, we say, sighed for new adventures. "Well, Tom, what is on your mind?" asked his father at the supper table that evening. "What is worrying you?" "Nothing is worrying me, Dad." "You are thinking of something. I can see that. Are you afraid your electric rifle won't work as well as you hope, when Ned comes over to try it?" "No, it isn't that, Dad. But I may as well tell you, I guess. I've been reading in the paper about a big elephant hunt in Africa, and I--" "That's enough, Tom! You needn't say any more," interrupted Mr. Swift. "I can see which way the wind is blowing. You want to go to Africa with your new rifle." "Well, Dad, not exactly--that is--" "Now, Tom, you needn't deny it," and Mr. Swift laughed. "Well, I don't blame you a bit. You have been rather idle of late."