Nami Matsushima (Meiko Kaji) is set up by her boyfriend, a crooked police detective named Sugimi (Isao Natsuyagi) to win favor with the Yakuza. She is raped by several drug dealers. She then makes a failed attempt to stab Sugimi on the steps of the Tokyo Metropolitan Police Headquarters.
She is sentenced to do hard time in a women’s prison. Matsushima is given the number 701. The prison is run by sadistic and lecherous male guards. The prisoners are forced to walk up and down a stair-like contraption naked with male guards watching from below. 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.
On the outside, Sugimi and the Japanese mafia orchestrate a plan in which Matsushima will succumb to an “accidental” death in prison. They enlist the help of Katagiri, pulling on her ties to both Sugimi and the mafia, and quickly set their plan in motion.
Matsushima is attacked in the shower but defends herself, wounding the attacker. She is punished by being held bound by ropes in solitary confinement. A group of trustees including Katagiri torments her. One of them torments her by pouring hot soup on her. Matsushima is able to trip the trustee and make her spill the vat of hot soup over herself, causing horrible burns. Matsushima is forced to dig dirt holes for two days and nights straight. She kills a woman who attempts to attack her during this digging by tripping her and breaking her neck. Matsushima is hung and tied from the ceiling while being beaten by her fellow prisoners.
After a riot, Matsushima escapes and kills all the Yakuza and Sugimi with a dagger. The film ends with Matsushima walking alone back in prison.