Mrs. Laetitia Rodd, aged 52, is the widow of an archdeacon who makes her living as a highly discreet private investigator. Her brother, Frederick Tyson, is a criminal barrister living in nearby Highgate with his wife and 10 children. Frederick finds the cases, and Laetitia solves them using her arch intelligence and her immaculate cover as an unsuspecting widow. When a case arises involving the son of the highly connected Sir James Calderstone, Laetitia sets off for Lincolnshire undercover as the family's new governess - quickly making herself indispensable. But the seemingly simple case - looking into young Charles Calderstone's inappropriate love interest - soon takes an unpleasant turn. And as the family's secrets begin to unfold, Laetitia discovers the Calderstones have more to hide than most.