For his first French-language film Losey cast Alain Delon as the titular anti-hero, an apolitical art dealer in Nazioccupied Paris startled to learn that he has a double – a Jewish refugee using Delon's identity to escape deportation and death. In search for his mysterious doppelganger, Klein sets in motion a dangerous, elusive process that ultimately endangers his own protected Aryan status – a striking return to the theme of lost identity first seen in The Servant. Delon's convincing reserve, similar to that of his steel-hearted criminals in Jean-Pierre Melville's thrillers, helps to make Mr. Klein one of Losey's bleakest and most frightening works. The cold dispassionateness of Mr. Klein's unmistakably critical attitude towards the virulent anti-Semitism of war-torn Paris makes the film even more unsettling.