In May 1940, the French army had suffered an astonishingly quick defeat against the Germans. As a consequence of the armistice signed in June 1940, France was divided into two parts bordered by the so-called line of demarcation. The northern part, including the entire Atlantic coast, was occupied by the Germans. The south, called "Zone libre", remained under French government. It was located at Vichy and headed by Word War I hero maréchal Pétain.

The film is set in Winter 1941 in a village divided by the demarcation line, which coincides with a river at this section. A bridge crosses the river. Everyone who wants two pass over has to plead his legitimation to the Germans, who have set up a military command on the northern side in the castle of count Damville (played by Maurice Ronet). The count, a captain of the defeated French army, returns home from war, multiply wounded. He can walk with the help of a cane only. But he is also morally damaged. He doesn't believe in the sense of resistance against the Germans any more, quite in contrast to his wife, the countess (Jean Seberg). She is British-born, listens every evening to the BBC broadcast to France and helps a British crew, whose plane has been shot down, to escape to Gibraltar.

The film offers a wide cross-section of possible behavior in times of occupation. There are collaborators, informers, résistance fighters, patriotic veterans from World War I, an upright doctor (Daniel Gélin) and a courageous teacher (Jean Yanne). The Germans are represented by an army major (Reinhard Koldehoff), who tries to keep his minimum standard of military decency, while two Gestapo agents act without any legal or moral inhibitions. The conflict rises to a climax when a British radio operator, working for the résistance, is found out and injured by the Germans. His comrades kidnap him from the hospital, and he hides at the teacher's house, where the countess nurses him. It turns out that the demarcation line not only cuts the French territory in two, but also segregates the French population into true patriots and vile cowards. The crossing of the bridge can also symbolize the change of moral sides.

This may seem a bit too clear-cut. Indeed, with the exception of the major, the Germans are represented in the usual stereotypes. But the the French, especially the count, are shown with their doubts and weaknesses. And there are situations where you have to chose between one of two possibilities. A good deal of suspense is generated by the permanent danger of being found out by the Germans. So this film offers not only moral instruction, but also exciting pleasure, conveyed by good performances of Ronet and Seberg.