Adopted samurai Seikei goes to the shogun's palace to view a demonstration of European medicine. Instead, he sees a murder as one of the foreigners dies of poisoning. Another of the foreigners wants to take away the young nephew of the dead man, but the boy is reluctant. He does not speak Japanese, so to keep him out of harm's way, Seikei's foster father tells Seikei to take him to the foreigners' base at Nagasaki. What seems like a simple task soon turns into a dangerous one, for many people seem to want the boy for their own peculiar purposes. Seikei has to use all his ingenuity and daring to carry out his mission and find the murderer as well.