Una Callingham witnesses her father's murder, causing her to lose all her memory. After four years, she recovers mentally but cannot recall her past. A new inspector provides her with newspaper clippings about the event, motivating her to uncover the truth. Determined and legally independent, Una embarks on a journey, following clues that take her to Canada, where the shocking details of the murder and the murderer's identity are revealed, keeping readers in suspense until the climax.