Le jeu de la vérité (1961)

A dozen of elegant people are gathered in a writer's desirable mansion. They all have got a secret to conceal. They begin a cruel game of truth, a game in which you are not supposed to tell lies. As the questions become more and more intimate and precise, the tempers rise while outside the storm is raging. Enter a hateful person who seems to know a lot about them. He's murdered. Who did it?