The novel’s main character, Maisie, is a private investigator who uses her knowledge of psychology as a key element of her practice. She pays close attention to body language and posture, even mirroring the stances of those around her to understand them or elicit confidences. She is in her early 30s when the novel opens and studied at Cambridge University after completing wartime service as a nurse. Maisie is tall and striking, with “eyes the color of midnight in summer” (3), while others note that the unusual color is matched by her perspicacity.

Maisie’s practice depends on her social connections with a noble benefactor, Lady Rowan Compton, and her mentor, Dr. Maurice Blanche. The mystery of her origins, revealed only in flashbacks, establishes that she was once a servant in the Comptons’ home, as her widower father was forced to abandon his dreams of sending her to school. However, her prospects changed when her unique intellectual aptitudes were discovered, and she was given private tutoring. Maisie regards books as fundamental to her well-being, feeling an “electric tingle of excitement” (87) as she faces the shelves of the Comptons’ large library.

Her ambition causes friction with her father and the other servants, especially her roommate, Enid, who is in love with the Comptons’ son but lacks Maisie’s intellectual aptitudes.