The protagonist and narrator of the novel is a young Nigerian nurse, Korede, who lives in an isolated mansion with her sister and mother and a single servant in Lagos, the capital of Nigeria. From the beginning, it is clear that Korede’s existence revolves around her younger and beautiful sister Ayoola, who is a serial killer of men. Korede has average looks and has always felt keenly that she is less attractive than her sister. More than that, within her nuclear family, Korede always had to take care of Ayoola; even their mother defines Korede only as a helpmate for her sibling. She also had to protect Ayoola from their frightening and abusive father. Protecting Ayoola has become the core of her identity.

The central conflict in the novel revolves around Korede’s attempts to attract the attention of a young and handsome doctor, Tade, and her consternation when he falls in love with her sister instead. Korede knows that her sister poses a lethal threat to Tade, and she must decide whether to protect her sister or do something to prevent her from murdering Tade. Because of her controlling nature, which she developed over years of working to protect her sister, Korede is not very popular amongst her coworkers at the hospital.