The two central characters of the film are Dr. Yasumoto (Yuso Kayama), the character we saw at the beginning of the film, and "Red Beard", Dr. Niide (Tosiro Mifune), the director of the clinic. The central story of the film is the development of Dr. Yasumoto from a spoiled, self centered, young jerk to a compassionate and dedicated doctor, under the gruff tutelage of Red Beard.
In a previous post I compared Kurosawa and Capra. Watching this film I thought of Kurosawa and Dickens. They both managed to combine a belief in the goodness of people with a totally bleak vision of the poor's plight, suffering under a callous and corrupt social system. This vision allowed them to alternate sentimental scenes with scenes of the blackest humor. This is not an action film but there is one fight where Red Beard explains to a bunch of pimps, who are trying to prevent the two doctors from removing a 12 year old girl from a brothel, that, “You know, a bad doctor can kill you. I won’t kill you, but I might break a couple of arms or legs." You should listen to your doctor.