One of the principal themes of The Housemaid Is Watching is the corrosive and harmful effect of secret-keeping on the dynamics of the Accardi family.

At the beginning of the novel, while Millie has close and open relationships with her husband and children, the family is shown hiding their true feelings to protect one another from possibly upsetting truths. For example, Enzo has never told Millie about the extent of his relationship with his former brother-in-law and mafioso Dario. Also, though Millie and Enzo feel excited about a new life in the suburbs, Ada and Nico have mixed feelings about the move; however, Ada, puts on a positive face for her parents.

In their new neighborhood, the Accardis begin to keep increasingly dangerous secrets from each other. When Nico and Enzo undergo intense behavioral changes as a result of the huge problems they are facing, they keep what is happening secret from Millie and Ada. Millie in particular misunderstands what is happening to her husband and son; without their honesty, she relies on insecurities about being a wife, mother, and middle-class person to guide her interpretation of their actions.

Eager to blend into the wealthy suburb, Millie wants her family to assimilate.