Ruth is an abnormally tall and ugly housewife whose husband, Bobbo, considers their relationship an open marriage based on convenience alone and only married her because he got her pregnant when they were teenagers.

Ruth plots her revenge on them, beginning by burning down her own house, therefore forcing the children to live with their father at Mary's lavish home which is a converted lighthouse.

Ruth, nonetheless feels slight sympathy for the secretary and encourages her to send a letter revealing the affair to Mary then arranges for her to take a new job in New Zealand so she can evade the police.

The stress and subsequent expense of his arrest after the problems created by unexpectedly being forced to share her home with Bobbo's children, pets and her mother has detrimental effect on Mary's physical and mental wellbeing, as a result her writing suffers, leading to further financial struggles.

Ruth uses her money to change her lifestyle and appearance, undergoing over several years, a series of surgeries to completely restructure her body to be identical to Mary.

[3][4] The novel was adapted in 1986 as an award-winning BBC television serial, starring Patricia Hodge as Mary Fisher, Dennis Waterman as Bobbo and Julie T. Wallace as Ruth, with only minor changes from the book.

The novel was adapted less faithfully by Hollywood in 1989 as She-Devil, starring Roseanne Barr as Ruth and Meryl Streep as her adversary, Mary.