París, 1968. Isabelle (Eva Green) y su hermano Theo (Louis Garrel), solos en la ciudad mientras sus padres están de viaje, invitan a su apartamento a Matthew (Michael Pitt), un joven estudiante americano, al que han conocido en un cine. Una vez en casa, establecen unas reglas para conocerse mutuamente, explorando emociones y erotismo a través de una serie de juegos extremadamente arriesgados.
Sinopsis en inglés:
Paris, spring 1968. While most students take the lead in the May 'revolution', a French poet's twin son Theo and daughter Isabelle enjoy the good life in his grand Paris home. As film buffs they meet and 'adopt' modest, conservatively educated Californian student Matthew. With their parents away for a month, they drag him into an orgy of indulgence of all senses, losing all of his and the last of their innocence. A sexual threesome shakes their rapport, yet only the outside reality will break it up.