In May 1968, the student riots in Paris only exacerbate the isolation felt by three youths: an American exchange student named Matthew (Michael Pitt) and twins Théo (Louis Garrel) and Isabelle (Eva Green). Having bonded over their mutual love of cinema, Matthew is fascinated by the sense of intimacy shared by Isabelle and Theo, who were born conjoined. When the twins' bohemian parents go away for a month, they ask Matthew to stay at their place, and the three lose themselves in fantasy.