On his way to start rehearsals at the Théâtre Montmartre, where he has been hired as male lead for a new production, young Bernard Granger tries to talk to an attractive woman, who repeatedly rebuffs him. When he arrives, she turns out to be the costume designer Arlette, a lesbian. He is taken to see the icily beautiful Marion, who is both owner of the theatre and leading lady. Her Jewish husband, Lucas, is believed to have left Paris but is in fact living in the cellar, where Marion visits him each evening to bring books and food and to talk about the new production. However, Marion is quite struck by Bernard, whom Lucas can just hear through a heating vent but never see. Unknown to anybody at the theatre, Bernard is a member of a Resistance group and delivers the bomb that kills a German admiral.
The first night is loved by a full house but one of the newspaper reviews next morning is viciously hostile, damning the show as Jewish. The writer, Daxiat, an anti-semite, hopes to oust Marion and take over her theatre. While cast and crew are celebrating their success in a nightclub, Daxiat is also there with another party. Bernard, furious that the man has insulted the gentile Marion, hustles him out to the street and pushes him around. Furious that Bernard has jeopardised her theatre, Marion refuses all contact with him offstage. One night, pretending to be air raid wardens, two Gestapo men start searching the theatre and it is Bernard to whom Marion turns in desperation for urgent help in concealing Lucas and his effects. When the Gestapo arrest Bernard’s Resistance contact just before they have planned to meet in a church, he decides to devote his life to the cause and give up acting. As he is clearing out his little dressing room, Marion comes in to say goodbye and the two make love on the floor.
After the war, Bernard returns to be male lead in a new play that the freed Lucas wrote while hiding. In it, the female lead played by Marion offers to share her life but he claims he never really loved her. At the end of the opening night, Bernard, Marion and Lucas stand hand in hand to receive the applause.