this is the third volume in the Motor Boys Series. The teens have a lot of money: in the first volume, they won a good deal of it by winning motor-cycle races; in the second volume, they shared in the proceeds of a gold mine in the west. But, who doesn't want more money, treasure and adventures? So, with their friend Professor Uriah Snodgrass, they turn their touring machine south in quest of a city with untold treasures said to have been buried centuries ago by an earthquake. But their enemy Noddy Nixon has heard of the treasure and tries to thwart them at every turn, including kidnapping Bob. And, the wild animals of Mexico, including jaguars, cougars and alligators threaten to end their trip a little early!