After being cruelly set up by a crooked detective named Sugimi, whom she loved, Nami Matsushima (aka Matsu the Scorpion) 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 who was committed for fraud and theft, Otsuka, jailed for burglary and extortion, and Katagiri who has been impounded for arson and illegally disposing of a body.