Dr. Karl Sternau, the personal physician of the count Bismarck, who spent much of his youth in Mexico, is sent back to that country during the occupation by French troops in the service of the Austrian ‘Emperor’ Maximilian, to carry an encouraging letter from U.S. President Lincoln to the nationalist Mexican president Benito Juarez. It’s good news, but there’s no cash- both men wonder whether that’s to be found in the legendary treasure of the Aztecs (hence the German title), the whereabouts of which an ancient priest has just disclosed to the female heiress of the Aztec imperial family. Meanwhile they turn for -promised- support to Mexico’s largest landowner, whose laborers are all Aztec descendants, count Don Fernando de Rodriganda y Sevilla, whose son and heir conde Alfonso is a gambling squanderer…