It tells a fictionalized story of a 17th-century diplomatic mission to "Nueva España" (New Spain or Mexico) by Japanese noblemen, and the cultural clash that ensues.
There they travel from Acapulco, crossing the desert until they reach Mexico City, where they realize they cannot carry out their mission.
However, since the Spanish authorities show no interest in their mission, they must continue on to Rome, to seek an audience with the Pope Paul V at the Vatican.
They end up returning home, crossing Spain and then Mexico again, and crossing the Pacific once more before arriving in Japan, where they discover that the new leaders of the country are now actively persecuting Christians and do not wish to have any commercial contacts with other nations.
The samurai Hasekura Rokuemon, who had traveled out of duty and not desire, ends up being ostracized.