Spending her holidays on the Swiss/Italian border, Margareta (Lina Romay) meets charming Sandra Mauro (Monica Swinn) and her husband. She agrees to stay in their house for the rest of her vacation, unaware that they are going to use her for smuggling diamonds over the border. There they get a little 'deeper' into knowing each other, but one night she awakens to strange noises and finds the couple brutally murdered in their living room. Margareta, deeply traumatized and unable to speak, is taken to Dr. Antonio's asylum. Antonio tries his very best to get her to speak and to reveal the events of the dreadful night. His attempts are not unselfish, since every member of the medical staff has already tried to be the first to find out where the missing diamonds are hidden. One night a mysterious black robbed person kills one of the nurses. Is this just a random attack or has somebody tried to get rid of a possible competitor. Only Margareta, who saw the killer, is able to uncover the mystery?