Des diamants pour l'enfer (1975)

At a marina, three masked men board a junk and seize a suitcase filled with diamonds. Shortly after the crime, the young leader of the trio, Perry Mendoza, methodically and cold-bloodedly kills his two accomplices, then returns to his partner, Shirley Fields, a nightclub owner, who shoots him dead. She then reports the incident to the police, claiming she acted in a fit of anger. As a result, she is sentenced to a relatively light term of just six years for a crime of passion, which she will serve in a women’s prison run by De Bries, a sadist who does not hesitate to have the inmates whipped. However, the insurance company that must pay for the diamonds that disappeared without a trace is not convinced of Field’s innocence and suspects a connection between her, the diamond theft, and Mendoza’s death. That is why insurance agent Milton Warren is sent there to investigate this dubious case. Warren then tries, with Bill—the millionaire’s henchman, who had in fact conspired with Warren to stage the theft as an insurance fraud and improve his financial situation, and had put an empty suitcase on the boat instead of the one supposed to contain the stones—to get their accomplice Shirley released from prison. Shirley had recruited the gangsters. Warren’s sudden appearance draws the interest of De Bries, the sadistic director of the women’s prison, who is convinced that Field knows where the precious stones are. To make her talk, he asks Martine, another inmate and his mistress, to get close to her, promising her a reduced sentence in return. Seeking comfort, Shirley begins an affair with Martine, and the two plan an escape. Since De Bries still does not know where the stones are, he decides to torture Shirley using electrodes attached to her genitals. She first violently gets rid of Martine, whose betrayal she has discovered, then takes De Bries hostage and thereby extorts a safe-conduct pass to leave the high-security prison. Once free, she is met by Warren, who is waiting with Bill. After Bill is eliminated—Shirley shoots him—she and Warren decide to make a fresh start in Mexico. In fact, the two of them had plotted the whole affair to get the diamonds. Separated from each other, the two criminals head at the end of the film to the agreed meeting place at the airport, with Warren carrying the stolen items.