“Well, that may be,” agreed Tom.  “I’m not saying it’s true.  Mr. Illingway is telling only what he heard.”

“Go on!  Tell some more,” begged Mr. Damon.  “Bless my shirt studs, this is getting exciting!”

“He says that the traveler told of this underground city of gold,” went on Tom, “though he had never been there himself.  He had met a native who had located it, and who had brought out some of the gold, including several of the images, and one he gave to the white man in return for some favor.  The white man took it to Africa with him.”

“But where is this underground city, Tom?” asked Mr. Swift.  “Doesn’t Mr. Illingway give you any idea of its location.”

“He says it is somewhere in Mexico,” explained the lad.  “The Africans haven’t a very good idea of geography, but some of the tribesmen whom the white traveler taught, could draw rude maps, and Mr. Illingway had a native sketch one for him, showing as nearly as possible where the city of gold is located.”

“Tom Swift, have you got that map?” suddenly cried Mr. Damon.  “Bless my pocketbook, but—­”

“I have it!” said Tom quietly, taking from the envelope a piece of paper covered with rough marks.  “It isn’t very good, but—­”

“Bless my very existence!” cried the excitable man.  “But you’re not going to let such a chance as this slip past; are you Tom?  Are you going to hunt for that buried city of gold?”

“I certainly am,” answered the young inventor quietly.

“Tom!  You’re not going off on another wild expedition?” asked Mr. Swift anxiously.

“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.”