Orgasmo Esotico (1982)

Buxom blonde Marina Frajese Lotar and her lover are enjoying sex at their remote country villa. Both are interrupted by Sonia Bennett, a mysterious black siren who stabs Lotar's lover in the stomach. Lotar attempts a feeble escape but is held down by Bennett, who injects her with a sleep inducing drug. Lotar wakes up to find Bennett sitting next to her and they call a doctor. Thats leads to a threesome...and the doctor not being able to ejaculate is murdered!