"I'm afraid I'll have to," answered his son with a smile.

"Go? Of course he'll go!" burst out Mr. Damon. "And I'm going with him; can't I, Tom?"

"Surely. The reason Mr. Illingway sent me the letter was to tell me about the city of gold. He thought, after my travels in Africa, that to find a buried city in Mexico would be no trouble at all, I suppose. Anyhow he suggests that I make the attempt, and--"

"Oh, but, Tom, just when I am perfecting my gyroscope!" exclaimed Mr. Swift. "I need your help."

"I'll help you when I come back, dad. I want to get some of this gold."

"But we are rich enough, Tom."

"It isn't so much the money, dad. Listen. There is another part to the letter. Mr. Illingway says that in that underground city, according to the rumor among the African natives, there is not only gold in plenty, and a number of small gold statues, but one immense big one--of solid gold, as large as three men, and there is some queer mystery about it, so that white traveler said. A mystery he wanted to solve but could not."

"So, dad, I'm going to search for that underground city, not only for the mere gold, but to see if I can solve the mystery of the big gold statue. And if I could bring it away," cried Tom in great excitement as he waved the missionary's letter above his head, "it would be one of the wonders of the world--dad, for, not only is it very valuable, but it is most beautifully carved."

"Well, I might as well give up my gyroscope work until you come back from the city of gold, Tom, I can see that," said Mr. Swift, with a faint smile. "And if you go, I hope you come back. I don't want that mysterious image to be the undoing of you."

"Oh, I'll come back all right!" cried Tom confidently. "Ho! for the city of gold and the images thereof! I'm going to get ready to start!"