During the Nazi occupation, Maurice Martin, a photographer lives with his wife Denise in Paris and strives by selling goods through the black market. One evening of September at 8 o'clock, he mysteriously turns into a woman. He quickly decides that his name will now be Héloïse. After searching for an explanation in books all night long, he turns back into himself at 8 in the morning. The next evening, the same incident occurs. Denise has more and more trouble adjusting to the change, mainly because his husband develops a crush on his female self that Héloïse reciprocates. But Héloïse feels lonely and gets out at night, meets a man, sleeps with him and gets Maurice into all sorts of troubles.