After being cruelly set up by a crooked detective named Sugimi (Isao Natsuyagi), whom she loved, Nami Matsushima (aka Matsu the Scorpion) (Meiko Kaji) is sentenced to do hard time in a women's prison, which is run by sadistic and horny male guards. There are 700 other prisoners, making Matsu number 701. Her crime was making a failed attempt to stab Sugimi on the steps of the Tokyo Metropolitan Police Headquarters because he used her to win favor with the Yakuza. While in prison she meets inmates like Yuki Kida (Yayoi Watanabe) who was committed for fraud and theft, Otsuka (Akemi Negishi), jailed for burglary and extortion, and Katagiri (Rie Yokoyama) who has been impounded for arson and illegally disposing of a body.