Charlotte Armstrong, Pt 3
The Unsuspected (1946; rpt 1967, 1970) opens with a man and woman discussing their impending revenge on the person whom they blame for their relative's death. Was it suicide or murder? To find out, they will infiltrate the man's household and do not care who will be used in the process.
Although this novel features one moment where the reader wishes to shake the heroine silly, it is a perceptive and disturbing look at how a twisted, charismatic personality can hold others in thrall. The Unsuspected was made into a movie (1947) starring Claude Rains, Constance Bennett, and Hurd Hatfield.