Eiji, Tatsuya Fujiwara, Sabu, and Nobuko Tomoko Tabata grow up as friends at the Kobunecho orphanage during the Edo period. Years later, Eiji is wrongfully accused of stealing a 100-ryo piece of gold cloth from the Watabun Bank and is sent to the Ishikawa Island workhouse. Refusing to speak, he earns the nickname Bushu from the head guard Tatsuo Yamada. Sabu loses his job as a paper hanger after repeatedly visiting Eiji and is sent out into the country, where he develops beriberi. Osue, Kazue Fukiishi, visits Eiji, and he explains that he believes Watabun and others framed him because they thought he planned to marry Watabun's daughter. He insists that he never intended to wed and that his only love is Osue, but he has devoted his life to revenge.
The geisha house where Nobuko works hopes to groom her to marry a 37-year-old Toku Yoji Tanaka and take over as mistress of the house, but Nobuko would rather run away with Sabu and Eiji. Osue visits her, and Nobuko accuses Osue of stealing the gold cloth. Sabu steals food from his employer and is fired again, forcing him to return to the city. Eiji breaks his leg saving another prisoner during the collapse of a frame under construction and emerges with a permanent limp. A heavy rainstorm threatens the Okawa River, risking a flood that could submerge the island and devastate the workhouse.
Disgraced pimp Roku, who repeatedly raped Nobuko and was responsible for the suicide of her older sister, runs into a burning building to rescue a girl there. Eiji convinces the prisoners to work together to reinforce the workhouse and protect it against the flood. The violent new prisoner Giichi, Grass Snake, attacks Eiji, but Eiji defeats him and his knife-wielding companion Ryu by striking them with his cherrywood cane; instead of punishment, the head guard sends Giichi and Ryu to Denmacho and is paid by Sabu to send Eiji to Kitamachi court, where his case is reopened with a petition signed by 100 inmates and he is set free.
Sabu and Eiji return to Nobuko's house, where the mistress has ended up marrying Toku. Nobuko asks Eiji to marry her, but he returns to Osue instead. Eiji discovers a letter of apology written by Sabu and becomes enraged, though Osue confesses that Sabu was protecting her and that she framed him for the theft because she wanted to marry him herself. Her father pleads with Eiji to punish him instead of her, but Eiji forgives her and takes Osue as his wife as she desired. Eiji later visits Sabu, who puts on a display of apologizing for the theft; Eiji punches him, then embraces him.
