Antoinette is upset when Rochester begins to call her Bertha. This new name comes after Rochester receives a very damaging letter from Daniel Cosway, who wants to hurt Antoinette. In the letter, Daniel asserts, among other things, that Rochester was tricked into marrying the daughter of a madwoman and that Antoinette has mad blood in her veins from both sides of the family. He also says that Antoinette has bewitched Rochester.

The letter plays on Rochester's insecurities, and he begins to believe it rather than Antoinette's version of her past (which, admittedly, is not altogether true either). Rochester is also increasingly unsettled by life on the islands, which he does not understand. Reading a book that discusses zombies and native ritual practices on the islands does not help. Rochester, at this point, believes he has been betrayed into a bad marriage that will ruin his life.

Rochester renames his wife with a British/Anglo-Saxon name to try to assert control over her. Renaming (as Robinson Crusoe names Friday) is a classic way for colonists to assert power and dominance over the colonized.

Rochester know Antoinette does not like the name Bertha, but he persists in using it because he is not a kind person. Using it foreshadows the way he will completely take over her life and force her to return to England with him—where he will keep her locked away.