A widow is looking for the drug that her deceased husband was hiding. While a policeman leads the investigation, other people try to find the famous product.

Guillaume Valmont has just died accidentally on the road. He leaves to his young widow, Isabelle, a prosperous herbalist's shop. On the day of the funeral, a beautiful, mourning stranger throws herself on the grave of the deceased, to the great astonishment of the audience. To avoid a scandal, the young widow takes the newcomer, Judith, to a café. She learns, with amazement, that her husband had a double life. When she returns, she finds the door of the herbalist's shop broken down and the apartment broken into. Nothing, however, seems to have disappeared. A young police inspector, Laforêt, who is sensitive to Isabelle's charm, leads the investigation.