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.

Mexico, 1864. The country is divided by the struggle against the French occupation and emperor Maximilian. The German doctor Karl Sternau and his friend Andreas Hasenpfeffer come to love the country and support the cause of the proud Mexicans.