Escaping the Measureless Cavern should have left Percy and Princess Portia free from Aztecs forever! But then the mountain loin, Puma, arrives in Aurora with worrying news. Rufus McGee, Percy's best friend in Pan Woods, is missing! Only Chitty Mantooth knows where he is, and he isn't telling.
Percy and Portia finally convince him to tell and then find themselves in more trouble than ever before. They discover that there is truth to the legend of a hidden treasure in the mountains near Pan Woods, only the treasure isn't in the mountains! They find that there is another entrance to the Measureless Cavern, and the Aztecs have found their way out -- not only found their way out, but are determined to reestablish their Aztec Empire in the Outworld! What is even more chilling is the fact that the Aztec Army has an advanced weapon that not even the U.S. Army can match.