In an old mansion, where tranquility is punctuated by the sounds of daily life, Colonel Arthur Bantry and his wife, Mrs. Bantry, discover an unbelievable and mysterious crime: the body of a blonde girl lies in the library, though no one in the mansion knows her. Amidst this atmosphere thick with secrets and shadows, a series of events unfolds that will turn the family's peaceful life upside down.

The story begins when the maid, Mary, finds the body in the library and rushes to Mrs. Bantry in shock, recounting what happened. Colonel Bantry, initially believing it to be a dream, is forced to confront reality and discovers that the crime is not what it seems.

While the police work to solve the mystery, Miss Marple, an expert in solving puzzles, begins her investigation. Mrs. Bantry accompanies her to the library where the body lies, embarking on a journey to uncover the secrets hidden within the mansion's walls. As the mystery deepens, the truth emerges, and strange connections between the crime and the family members become apparent. In this suspenseful and mysterious novel, a complex picture is painted of family relationships, secrecy, and justice, with a focus on the human psyche in the face of difficult situations.