Clumsy, put-upon Ruth Patchett leads a drudge's life with her two bratty children Nicola and Andy, and her neglectful accountant husband Bobbo. When Bobbo starts an affair with his top client, the glamourous, lighthouse-dwelling romantic novelist Mary Fisher, Ruth does everything she can to be a good wife but everything fails and Bobbo humiliates her in front of his parents before leaving her for Mary. Ruth snaps and, declaring that she will become a she-devil, burns the house down in such a way that the insurance claim will be invalid and dumps the children on Mary and Bobbo.

Whilst Mary and Bobbo find it tough going looking after the kids, Ruth, calling herself Lily Latimer, becomes a care assistant at the home where Mary's mother lives. Having befriended a co-worker, Nurse Hopkins, Ruth soon gains the down-to-earth Mrs Fisher's trust, learning that she regards Mary as being 'from the gutter'. Soon, Ruth has stage-managed the old lady's discharge into the unwilling care of her daughter, whose work suffers from her unwanted new family.

Looking increasingly more elegant and visiting Harley Street with a view to plastic surgery, Ruth opens her secretarial agency Vista Rose with Hopkins. By chance, Bobbo's firm requests two of their temps and Ruth knows just who to send along, a bimbo whom he will love and leave seeking revenge and a computer hacker. Between them, they frame Bobbo for embezzlement though the money he has supposedly stolen ends up in Ruth's account.

Her romance in tatters, Mary turns for help to lonely, well-meaning Catholic priest Father Ferguson. She is not to know that Ruth, having given Vista Rose over to Hopkins, has installed herself as the priest's atheist housekeeper Molly, who also introduces him to sex, convincing him that love does not exist so that the only comfort he gives Mary is cynical and carnal.