As the film opens, we see a terrified young woman named Margarita (Lina Romay) being removed from a home where a couple lie dead in a pool of their own blood. Deeply traumatized and unable to speak, shes taken to Dr. Antonio's psychiatric clinic.
Antonio tries his best to get her to speak and reveal the events of that dreadful night. And he's not alone in his efforts, since other members of the medical staff -- namely Dr. Farkas and his lascivious wife, Irina -- are also trying to be the first to find the missing diamonds the slain couple were known to be smuggling!
One day a sinister black-robed person murders Nurse Helga and rapes Margarita, whom she had been following. The killer soon returns to murder and then rape the warm body of Petra, a lesbian patient enlisted by the Farkas' to seduce information from Margarita.
This latest attack shocks Margarita back to full awareness, and she relates the events that led to the murder of the Mauros:
Margarita Martin was on holiday at Lake Maggiore [incorrectly referred to in the film as Lake Como] where she met a bisexual alcoholic named Sandra Mauro (Monica Swinn) and her manipulative guitar-playing husband, Carlo. She agreed to stay in their home for the rest of her vacation, unaware that they would use her to smuggle diamonds across the border. During her stay they got to know each other quite intimately. But one night she awakens to strange noises and finds the couple brutally murdered in their living room by a man in a black robe. All she remembers of him are his eyes, which looked like those of Dr. Antonio.
Dr. Farkas tells her she's cured, and can soon leave the clinic -- revealing that the two murders she witnessed there were simply ruses, meant to shock her back to sanity. The Farkas' go home to "celebrate" having learned the location of the diamonds. Meanwhile, Dr. Antonio gives Margarita a good shagging to celebrate her last night at the clinic.
But now its time to get the diamonds ... and eliminate all the witnesses!