Lana Turner takes the lead in the seventh film version of Alexandre Bisson's glossy soap opera. Holly Parker (Turner) is married to respected diplomat Clay Anderson (John Forsythe), but his busy schedule prevents them from seeing each other very often. Distracted and lonely, Holly allows her head to be turned by carefree playboy Phil Benton (Ricardo Montalban), who dies in a freak accident during an assignation. In a panic, Holly contacts her mother-in-law, Estelle Anderson (Constance Bennett) and asks what she should do. Estelle, a joyless woman who has never cared for her daughter-in-law, tells Holly that unless she wants to destroy her husband's life and career, she should flee the country and never return. Tearfully, Holly follows Estelle's advice, leaving behind her young son. Many years later, Holly has fallen on hard times; addicted to drugs, she scrapes out a meager living as a prostitute in a cheap hotel in Mexico. Devious criminal Dan Sullivan (Burgess Meredith) tries to involve Holly in a blackmail scheme; at the last minute, she finds out that Clay is the target, and she kills Sullivan. She cannot afford to hire a lawyer to defend her, so she is assigned a dedicated young public defender, whom she soon recognizes as her son, Clay Anderson, Jr. (Keir Dullea). Not wanting Clay, Jr. to know her true identity, Holly is tried as "Madame X," but she has trouble keeping her composure given the trial and her mixed joy and shame at seeing her son. Madame X was Constance Bennett's first film in 12 years and the last she would ever make; she died of a cerebral hemorrhage shortly after completing her work on the picture, nine months before it was released.