Nami Matsushima is used as a spy by her first real boyfriend, a police detective named Sugimi, to investigate a
drug smuggling ring. However, her role is discovered and she is raped by several drug dealers. It emerges that Sugimi was simply using Matsushima as a pretext to obtain a bribe from the
yakuza. Seeking revenge, Matsushima 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, where her prisoner number is 701. The prison is run by sadistic and lecherous male guards. Prisoners are forced to walk up and down metal scaffolding naked with male guards watching from below. While incarcerated, Matsushima meets inmates like Yuki Kida, who was convicted for fraud and theft; Otsuka, jailed for burglary and
extortion; and Katagiri, who was imprisoned for
arson and illegally disposing of a body. Outside the prison, Sugimi and the yakuza orchestrate a plan in which Matsushima will succumb to an "accidental" death in prison. The conspirators enlist the help of Katagiri 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 talkative female prisoner tries to get information from her, but Matsushima remains silent. When the woman advances on her, Matsushima seduces her into a sexual encounter. The prisoner is revealed to be a rookie policewoman sent by warden Goda as a spy, but her passion for Matsushima turns her against the prisoner staff, and the angered Goda becomes determined to break Matsushima. A group of trustees, including Katagiri, tortures Matsushima; one pours 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 consecutive days and nights. She kills a woman who attempts to attack her during this digging by tripping her and breaking her neck. In response, Matsushima is hung and tied from the ceiling while being beaten by her fellow prisoners. After a
prison riot, Matsushima escapes and kills Sugimi and all of the yakuza with a dagger. As the film ends, Matsushima strides alone down the prison corridor. ==Cast==