Marc de Segur is approached by his longtime acquaintance Joseph de Menard, he asks to investigate the death of his aunt Baroness de Morel, who recently died in a street robbery. Not considering it possible to refuse the man who once saved his life, Mark takes on this investigation, and soon becomes convinced that the initial version is incorrect, and behind the usual robbery lies a coldly thought-out and executed murder. In addition, when communicating with the victim’s relatives, Mark every now and then sees the lines written by her, which gradually form into a posthumous message hiding the secret of the killer.