Hand of the Assassin(1967)

Original title: El rostro del asesino

A group of people take shelter from the storm in an old spa served by a marriage and a servant. It is a very diverse group, highlighting a man who, with his wife, carrying a briefcase full of money. At night, at dinner in honor of the newcomers is a power outage and shortly afterwards, they realize that the man with the briefcase has been murdered.