Millie Accardi, formerly Wilhelmina Calloway, is the protagonist and primary narrator of The Housemaid Is Watching. She is the wife of Enzo Accardi and the mother of Ada and Nico. In the first two novels in the series, Millie worked as a housemaid for various wealthy families, which frequently led to dangerous situations as her employers found out about her past: When she was a teenager, Millie spent 10 years in prison for killing a fellow teen who tried to rape her friend. Like Enzo, Millie feels a strong motivation to protect women from dangerous and abusive men, which guided her actions in the first two novels. In this third installment, however, Millie’s stress and fixation on Enzo’s actions and Nico’s behavioral changes lead her to miss the signs that Martha needs similar help.

Millie’s stress plays a huge role in her character development, as her blood pressure problems are symbolic of the danger her family is in. As soon as they move to Locust Street, she develops blood pressure problems. She can sense that danger is present for her family, but she cannot identify its source. After Jonathan’s death, her blood pressure returns to healthy levels.