In restless 1930s Paris, the American sisters and spiritual mediums, Laura and Kate Barlow, are an authentic psychic act touring pre-war Europe. Indeed, such is their reputation, that sceptical but curious spectators join them on stage, eager to experience a hypnotic séance with the dearly departed. As one thing leads to another, the French film producer, André Korben, dazzled by the sisters' extraordinary psychic ability during a performance, decides to enlist their help, in high hopes of capturing even the faintest suggestion of a real paranormal manifestation. Little by little, World War II creeps in, and Korben's prestige rests entirely on the success of this single effort. But, are the Barlow Sisters nothing but an elaborate hoax, or do they genuinely possess the dark gift?