Tom Swift in the City of Gold
Victor Appleton
 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. In Mexico, they hire a team of Mexicans who catch onto the city of gold plot and chase after it in competition with Tom as well as the Foger's. To make things worse, Tom had been warned about "Head Hunters" by his missionary friend. After finding the underground city and losing the trail off the two competing parties, Tom's gang end up accidentally sealing themselves into the city for about a week. They finally escape when their enemies release them unintentionally. The Foger's and the Mexican team show up at the entrance with the escort of the Head Hunters. By trying to get in, they let Tom and his team out. Before the others can explore the city, an underground river floods it and they make off with a huge wealth of salvaged gold.