In 1950, at a French army hospital in French Indochina, nurse Athena Roberts, the level-headed daughter of an American diplomat, anticipates her last day on the job before joining her father in Hanoi, while nurse Joy Brooks, a cynical Englishwoman who holds the entire camp in contempt, eagerly awaits a weekend leave in Hanoi. As Dr. John Richter, the homesick surgeon, prepares to operate on a patient, the hospital is besieged by a band of bloodthirsty guerrillas led by Chen Panok. After savagely killing Dr. Richter's patient, Chen takes Richter, his colleague Dr. Jacques Minelle and all the nurses prisoner and leads them into the jungle to treat Gung Sa, the ailing warlord and leader of the guerrillas. Knowing that Chen and his men despise the Christian religion, Chioko, one of the nurses, dresses Sister Marie, an emotionally frail nun, in a nurse's uniform to conceal her identity. Before leaving, the guerrillas crucify Sister Magdalena, the one remaining nun. Upon reaching the guerrillas' fortress, which is regarded as impenetrable because it is guarded by five gates, Richter examines Gung Sa and announces that he needs two days to conduct a series of tests. Chen, enthralled by the blonde Athena, orders her to his room, where he offers her gifts and informs her that he wants her as his woman. After Chen offers Athena time to consider his proposal, Joy encourages her to accept his offer, asserting that God intended women to use sex for their survival. When Richter decides that Gung Sa must be operated upon, the warlord instructs his minions to burn the medics if they fail. After determining that Gung Sa has a malignant tumor and faces certain death, the married Richter realizes that he has nothing left to lose and so he tells Athena, who is in love with him, that he has feelings for her. Once the operation is completed, Chen assembles the nurses and declares that they will now serve as sex slaves to his men. Turning to Richter, Chen offers him first pick of the women, and to protect Sister Marie's virtue, he chooses her. Chen then claims Athena, and when she resists his advances, he brutally rapes her. Determined to break out of the fortress, Richter schedules another operation on Gung Sa as a cover for the escape. While Richter drugs the guard in the operating room, Chioko flirts with another and Athena distracts Chen by pretending to seduce him. When Chen responds to Athena's charms, she seizes his gun, shoots him, then flees. As the nurses assemble in the courtyard, Richter and Minelle are gunned down by the guerrillas. Kneeling, Athena tenderly kisses Richter farewell, then picks up a machine gun and kills several of the guerrillas. Greta, a German nurse whose late husband was a solider, then instructs the nurses in the handling of machine guns and grenades. Pulling himself up from the floor, Chen runs into the courtyard, his machine gun blazing, and in their haste to flee, the nurses leave several guns behind and plunge into the cover of the jungle. After making camp that night, Joy cautions the women never to reveal that they were sexually assaulted and then discloses her own fate as an outcast after the Japanese captured her during World War II and forced her to work in a house of prostitution. The next day, the women make their way to a bridge. When two guerrillas unexpectedly appear from the jungle and lunge at them, Suzette, the desperately unhappy matron nurse, pulls the pin from a grenade and accidentally detonates herself. Suzette's demise startles the guerrillas, allowing the women to overtake them. When a shaken Joy chastises Marie for standing by while the others fight for their lives, Marie resolutely picks up one of the dead guerrilla's guns. As the nurses trudge down an abandoned road, Chen, who has tracked them through the jungle, spots them from a ridge above and roars that Athena will pay for her lies. When Chen leads his men in a charge, the nurses resolve to climb the mountain to freedom, and Athena hurls several grenades at Chen, slowing him down. Some time later, the women come across a deserted village whose only occupant is an old, dying woman. When one of Chen's scouts locates the women, Athena vows to remain behind and kill Chen, prompting the others to decide to stop running and face their tormentors. The women urge Marie to continue on to freedom, but after she declares that she is unworthy of the habit and cannot face going home, the women agree to let her stay if she will don her habit once more. As Chen nears the village, Athena, crazed with vengeance, taunts him. One by one, the women are downed by the guerrilla's gunfire until only Marie and Athena are left standing. Marie then defiantly confronts Chen, thus sacrificing her own life so that Athena can find a gun to defend herself. After peppering Chen with a blast of bullets, Athena contemptuously stands over his dying body as he proclaims his love for her. Athena then determines that Joy and Greta are still alive, and while she dresses their wounds, she confides that she is pregnant with Chen's child.