Google translated from Wikipedia: (SPOILERS)
Silvia runs a small hotel with her rich husband Paolo, who is older than her, but the marriage is in crisis. Paul thus consoles himself with a steady lover. One day, after giving his lover a ride in the car, Paolo runs into Alessio. Alessio is unharmed while Paolo, in an attempt to avoid running into him, is seriously injured and loses his sight. During her husband’s hospitalization, Silvia hires Alessio as a driver, becoming his lover too. Paolo, still blind, is discharged from the hospital and returns to the hotel. Paolo continues to receive visits from his lover. Silvia, annoyed by her husband’s behavior, devises a plan to kill him with Alessio’s complicity and take possession of her possessions. Alessio is initially against the idea of committing a murder, but increasingly seduced by Silvia’s seduction, he agrees to become an accomplice in the criminal act. Meanwhile, Paolo recovers his sight but keeps Silvia in the dark and, thus found out about the relations and agreements between Silvia and Alessio. The two decide to eliminate Paolo during a boat trip but, at the moment to act, Alessio fails, overcome by a sense of pity.
Under Silvia’s insistence, a few days later the two lovers lead Paolo to the edge of a cliff, convinced that the man is still blind. When they understand that he has recovered his sight, the tension rises. Alessio pushes the man into the escarpment, preventing Paolo from attacking them first. Cosetta, hotel attendant as well as Alessio’s occasional lover, senses the couple’s intentions and begins a game of blackmail. Cosetta has well understood that it was Silvia and Alessio who killed Paolo. Cornered by repeated blackmail, Silvia convinces Alessio to make an appointment with Cosetta at the port. Once Cosetta reaches the place, Silvia appears in front of Cosetta, and without any mercy, kills Cosetta with a pistol.
Once Cosetta has been eliminated, Silvia orders Alessio to get rid of the body and he, increasingly at the mercy of Silvia, proceeds to execute but, on his return to the hotel, he is killed by a few gunshots fired by Silvia. This will make both murders fall on Alessio and exonerate herself by claiming to have killed Alessio in self defense. At the base of Silvia’s gesture there are certainly reasons of economic interest: after the departure of Paolo and Alessio, Silvia remains the only heir of her wealthy husband, but the blind jealousy of the woman was also of great importance. Silvia cannot tolerate the relationship between Alessio and Cosetta. Extremely rich and free from all ties, Silvia finds herself walking by the sea in front of the hotel but she is less free than she thinks, more and more a prisoner of her blind frustration than ever.