In 1820, young Dr. Yasumoto, returned to Edo after graduating from Dutch medical school in Nagasaki. He presented himself at the public clinic managed by Dr. Niide ( Toshiro Mifune ), aka Akahige ( Red Beard ) because of the color of his beard, thinking it was a courtesy call arranged by his father, also a physician .
It turned out he was expected to work there for a while. Yasumoto didn't find anything to his liking. All doctors' bedroom were not on the sunny side ( that was for the patients ), there's no heat & no tatami ( Japanese comfortable bedding ). Extremely upset & frustrated because he had hoped to find a prestigious post as a shogun's personal physician, Yasumoto rebelled by not doing what he was supposed to do. He didn't wear the doctor's uniform, he lied on the lawn in front of an isolated ward reserved for a murderous female mental patient ( where he was already warned not to come near by ). He hated the food, drank sake though it's not permitted, found the patients stank ( which one of his colleague at the clinic called " the smell of poverty "). In short, he's too good for this under-funded public clinic. He obviously hoped his immature benavior would have earned his own dismissal by Dr. Niide.
One night, the mental patient escaped from her ward & while Dr. Niide & nurse Osugi went out looking for her, the Mantis ( the mental patient's nickname ) showed up in Yasumoto's bedroom. She told Yasumoto the story of her life, how men had raped her many times since she was 9 year old & they threatened to kill her if she ever denounced them. After a few years, she had enough of all the sexual abuse and killed three men ( thus the name Mantis). During the course of the conversation, she managed to seduce Yasumoto but with intention to kill. Dr. Niide came back in time to save the young doctor & excused him for being drunk & for his weakness, as all other men, in front of pretty women. According to Dr. Niide, the Mantis was just born that way
Little by little, Yasumoto started to integrate into the workforce at the clinic. For his 1st assistance in the operating room, he couldn't stand it & fainted. Yasumoto discovered Dr. Niide, eventhough looked stern & appeared difficult, had a kind heart. He managed to get a bit of money to help a patient's destitude daughter with 3 small children ( the old man just passed away before her arrival ). He gave her 5 ryos ( 1 gold ryo = USD$150 today ). Later he said that he was able to get that money from the magistrate & also got him to drop charges against her for attacking her husband. Gradually, Yasumoto started to put on the uniform.
When Dr. Niide learnt that funds for the clinic were cut, with Yasumoto in tow, paid a visit to an obese wealthy lord. He ordered a lean diet for the man & charged him 50 ryos, instead of the usual fee of 30. On the way back to the clinic, they paid a visit to a brothel to see a patient with syphillis. There they discovered the madam & her servant were getting a 12 year old girl ready, by way of beating, to receive customers. Dr. Niide had to use force to defeat a dozen thugs working for that madam in order to bring the girl Otoyo to the clinic.
He then assigned Yasumoto to care for the girl because not only she was sick but also displayed abnormal behavior ( she kept wiping the floor without stopping when she was not feverish ). Otoyo at first refused to be cared for but gradually with Dr. Niide's patience, she started to accept drinks & medicaments.
All the while, Yasumoto had a visitor named Masae. She was Yasumoto's ex-fiancee's sister. At 1st, he refused to see her but 1 day when Yasumoto stepped out of the clinic, Masae was already waiting at the gate, hoping to see him. Subsequently, he invited her inside. Seeing Otoyo wearing torn clothes, Masae brought her some nice clothes but realizing that Masae drew away Yasumoto's attention, the little girl became jealous & threw the new clothes into the mud. She was scolded by the female orderlies but Dr. Niide wisely saw that even though Otoyo wanted Yasumoto for herself only then but with time, she would have developed into loving others as well.
One day, while Osugi had an intimate moment with another doctor at the clinic, the madwoman tried to kill herself by hanging. Her father came & scolded Osugi severely. Dr. Niide came to her defence & reprimanded the father for not caring enough for his daughter & had let strangers taking charge.
Another day, there's a little boy who sneaked into the clinic kitchen, trying to steal some food. Otoyo befriended the kid, gave him food & asked him not to steal anymore. Some time later, the boy came to say goodbye, saying he & his parents plus 2 brothers were leaving for a better place. Otoyo was too young to suspect anything, believing they had some rich relatives who could help them out. Pretty soon enough, the whole family was brought in on the brink of death because they had swallowed rat poisoning, trying to kill themselves. The boy & his parents were saved but his 2 brothers perished.
Dr. Niide brought many good news to Dr. Yasumoto. Masae's parents proposed the young physician to marry Masae & forgive her sister. Their father, because of the broken engagement, had forbidden Masae's sister to set foot back to his house. Now since she gave birth to a baby, he wanted to forgive her in order to be able to see his grandchild. Yasumoto also was promised a post under a shogunate's wing.
Yasumoto expressed remorse & regret with Dr. Niide for being haughty & arrogant upon his arrival at the clinic. He regretted also of suspecting Dr. Niide's intention when Akahige wanted to see his notes. He had learned how to become a real doctor, not only with his knowledge in medecine but how to help others who were much less fortunate than he was - in short, how to be a compassionate doctor.
At their wedding ceremony, Yasumoto announced to Masae, in front of their parents & Dr. Niide that he wished to inform her that if she wanted to become his wife, she should be prepared for a life without honor & money because he had decided to continue to work at the clinic of Dr. Niide