What Have You Done to Solange? (1972)

In London, Italian gym teacher Enrico 'Henry' Rosseni is having a love affair with his 18-year-old student Elizabeth, who is the niece of the owner of the Catholic school where he works and she studies. His estranged wife Herta is the Music and German teacher. One day when Enrico and Elizabeth are in a boat in a grove, she sees a man hunting down a woman. Enrico believes she's making it up, but the next morning, he learns that a teenager was murdered in the river bank in the grove. Inspector Barth goes to the school since the victim Hilda studied there, and Enrico is soon the prime suspect, though Elizabeth could give him an alibi. When a second student is murdered, and then so is Elizabeth, Enrico decides to investigate, and he teams up with Herta to find the of the mysterious Solange, but what happened to Solange?