A pair of resourceful young sisters and their friends become detectives when strange noises, mysterious visitors, and odd notes disturb their neighborhood. They follow clues through midnight summons, stormy chases, cellar searches, and a futile pursuit, uncovering hidden meetings and a secret that culminates in the apprehension of a suspect. Episodes combine household scenes, kitchen banter, and outdoor adventure, with suspense punctuated by small discoveries and practical problem-solving. The narrative moves episodically through short chapters and illustrations, balancing light domestic moments with growing peril until the mystery is explained and resolved.