The film takes place in Koishikawa, a district of Edo (the former name of the city of Tokyo), in the 19th century. Young Dr. Noboru Yasumoto (Yūzō Kayama) is the film's protagonist. Trained in a Dutch medical school in Nagasaki, the arrogant Yasumoto aspires to the status of personal physician of the Shogunate, a position currently held by a close relative; his father is already a well-established, highly competent physician. Yasumoto believes that he should progress through the safe, and well-protected, army structure of medical education. However, for Yasumoto's post-graduate medical training, he has been assigned to a rural clinic under the guidance of ''Akahige'' ("Red Beard"), Dr. Kyojō Niide (played by Toshiro Mifune). Dr. Niide may seem like a tyrannical task master, but in reality he is a compassionate clinic director. Initially, Yasumoto is livid at his posting, believing that he has little to gain from working under ''Akahige''. Dr. Yasumoto feels that Dr. Niide is only interested in his medical notes and soon rebels against the clinic director. He refuses to wear his uniform, disdains the food and spartan environment, and enters the forbidden garden where he meets "The Mantis" (Kyōko Kagawa), a mysterious patient that only Dr. Niide can treat.