The Silk Worm (1974)

Smeralda Amadier, a retired singer, lives in an isolated villa with her secretary Marcella and her lover Didier (but throws out the latter after catching him with another woman). Smeralda has huge debts and when creditors threaten her with bankruptcy she decides to sell her valuable jewels. That evening, she meets Costas, a handsome young man who seduces her. Next morning, there is no sign of him or the jewels. He was apparently a penniless gigolo, but who was his secret partner in the theft?