High-spirited young Tom Swift is off on another of his many exciting adventures. This time he's in search of gold in an underground lost city. Tom finds the lost city in a remote area of Mexico, and he finds the gold. Getting into the city was difficult for the adventurers, but when they try to get out, then their real adventure begins. Tom and his companions find themselves trapped in an underground city which contains as many traps and mazes as an Egyptian pyramid.

He was too much engaged in reading the missive for no sooner had he perused the first few lines than his eyes began to open wide in wonder and his manner plainly indicated his surprise. He read the letter once and then over again and when he had finished it a second time he made a dash for the house.

Tom receives a message from his missionary friend which describes a wonderful lost city, filled with treasures of gold, somewhere deep in the heart of Mexico.

Unlike some other reproductions of classic texts (1) We have not used OCR(Optical Character Recognition), as this leads to bad quality books with introduced typos. (2) In books where there are images such as portraits, maps, sketches etc We have endeavoured to keep the quality of these images, so they represent accurately the original artefact. Although occasionally there may be certain imperfections with these old texts, we feel they deserve to be made available for future generations to enjoy.

Tom receives a message from his missionary friend whom he saved from captivity in Africa during the adventures of the preceding volume. The message describes a wonderful underground city, filled with treasures of gold, somewhere deep in the heart of Mexico. Not one to turn down adventure, Tom accepts the challenge to find the lost city. Around this time, Andy Foger and his father had lost their fortunes and are off after Tom's trail in order to steal the treasures from him. In order to make the trip possible, Tom must remodel his previous airship- a hot air balloon with an enclosed cabin. Accompanying him on the journey is Ned Newton, Mr. Damon, and Eradicate. They set off on a tramp steamer to Mexico. On this steamer, they uncover two mysterious passengers who they confirm to be the Foger's.

Victor Appleton was a house pseudonym used by the Stratemeyer Syndicate and its successors, most famous for being associated with the Tom Swift series of books. The following series have been published under the Victor Appleton name: Tom Swift (1910-1941), Motion Picture Chums (1913-1916), Moving Picture Boys (1913-1922), Movie Boys (1926-1927), Don Sturdy (1925-1935), Tom Swift, Jr. (1954-1971) (technically, ""Victor Appleton II""), Tom Swift (Third Series) (1981-1984) and Tom Swift (Fourth Series) (1991-1993). Contract authors of these books writing under the name ""Victor Appleton"" included James Duncan Lawrence, Howard Roger Garis, John W. Duffield, W. Bert Foster, Debra Doyle with James D. Macdonald, F. Gwynplaine MacIntyre, Robert E. Vardeman, Thomas M. Mitchell.