Kill Me Quick, I'm Cold(1967)

Giovanna and Franco are lovers pretending to be brother and sister in order to con unsuspecting marks while staying in the most luxurious locales throughout Europe. In their travels, they come across the beautiful Christina, a girl who is being threatened by her brother, Sergio, in order to get the family fortune. But as Giovanna and Franco delve into their story, the double-crossing begins, and no one is sure who is getting tricked.