Dr. Cordelier, living in a suburb of Paris, withdraws from society to pursue research into the functioning of the human brain. His lifelong friend, Maître Joly, becomes concerned when Cordelier draws up a will that bequeaths his entire estate to a stranger, Monsieur Opale; he cannot understand why Cordelier defends him, considering Opale attacks women and children. After a colleague is killed, Joly confronts Cordelier and discovers the truth behind his friend's behavior.

New Europe presidential candidate Etienne Alexis is a scientist promoting artificial insemination for social betterment and therapy to eliminate passion. To celebrate his engagement to a cousin, he hosts an aseptic picnic, where Mother Nature asserts herself. A shepherd's flute conjures a windstorm throwing Alexis together with the luscious Nénette, a farm lass who, although unimpressed with men, wants to have a baby.

Police Commissioner Jules Maigret returns to the small village where he spent his childhood at the request of the Countess of Saint-Fiacre, who has received a disturbing anonymous letter.