A middle-aged spinster takes a large country house for the summer with her nephew and niece and soon encounters a series of uncanny intrusions, disappearances, fires, and stolen documents tied to a local bank. Drawn into detection by circumstances, she and a detective trace secret passages, hidden rooms, and physical clues such as a misplaced ladder and a hole in a wall. Personal histories and concealed identities surface as suspects are followed and witnesses interviewed, and the narrative resolves through assembling tangible evidence and testimonies that reveal the motives and methods behind the criminal plot.