context: Joanna Eberhart (Katharine Ross) is a young wife who moves with her husband Walter (Peter Masterson) and two children from New York City to the idyllic Connecticut suburb of Stepford. Loneliness quickly sets in as Joanna, a mildly rebellious aspiring photographer, finds the women in town all look great and are obsessed with housework, but have few intellectual interests. The men all belong to the clubbish Stepford Men's Association, which Walter joins to Joanna's dismay. Neighbor Carol Van Sant's sexually submissive behavior to her husband Ted, and her odd, repetitive behavior after a car accident also strike Joanna as unusual.
  
  
  
  
  Joanna and Bobbie investigate Stepford.
  Things start to look up when she befriends another newcomer to town, sloppy, irrepressible Bobbie Markowe. Along with the glamorously beautiful tennis playing trophy wife Charmaine Wimperis, they organize a Women's Lib consciousness raising session, but the meeting is a failure when the other wives hijack the meeting with cleaning concerns. Joanna is also unimpressed by the boorish Men's Association members, including intimidating president Dale "Diz" Coba. Stealthily, the Men's Association collects information on Joanna including her picture, her voice, and other personal details. When Charmaine returns from a weekend trip with her husband as an industrious, devoted wife who has fired her maid and destroyed her tennis court, Joanna and Bobbie start investigating, with ever-increasing concern, the reason behind the submissive and bland behavior of the other wives.
  Bobbie and Joanna start house hunting in other towns. Later, Joanna wins a prestigious contract with a photo gallery with some photographs of their respective children. When she tells Bobbie her good news, Joanna is shocked to find her freewheeling friend has abruptly changed into another clean, conformist housewife, with no intention of moving from town. Joanna panics, and, at Walter's insistence, visits a psychiatrist to whom she voices her belief that the men in the town are in a conspiracy of somehow changing the women. The psychiatrist recommends she leave town until she feels safe, but when Joanna returns home, the children are missing. Joanna and Walter argue and get into a physical scuffle. In an attempt to find her children, she thinks Bobbie may be caring for them.
  Joanna, still mystified by Bobbie's behavior, becomes increasingly desperate and stabs Bobbie with a kitchen knife. Bobbie doesn't bleed but goes into a loop like a malfunctioning computer, thus revealing the real Bobbie has been replaced by a fembot. Despite sensing she may be the next victim, Joanna sneaks into the mansion which houses the Men's Association to find her children. There, she finds the mastermind of the whole operation, Diz Coba, and eventually her own robot-duplicate. Joanna is shocked into paralysis when she witnesses its soulless, black, empty eyes. The Joanna-duplicate brandishes a stocking and approaches Joanna, implying that she will be strangled.
  At the film's end, the Joanna duplicate is seen placidly purchasing groceries at the local supermarket, along with the other "wives," saying little more than hello to each other. In the background, a black couple (new residents of Stepford) argue and it's likely the wife is poised to become the conspiracy's next victim. Still images show a cheerful Walter along with his children in the back of the station wagon, picking up his wife from the supermarket.
question: Who turns overnight from tennis fan to devoted wife?
answer: Charmaine