In the midst of World War II, Julien Quentin leaves his mother and Paris to travel to a Catholic boarding school in the country. Upon arrival, he meets Jean Bonnet, the new
Julien and Jean in the forest
boy who claims to be Protestant, and, though hostile at first, begins to befriend him. He is the only boy who discovers his new friend's secret: that he is a Jew named Jean Kippelstein hiding from the Gestapo.

The turmoil in France at the time is apparent in this film through several instances. First, there are two air raids during which the students must hide in a sheltered basement underground. Collaborators search the school at one point looking for shirkers from German work camps. Also, when Jean and Julien get lost in the woods during a "boy scout game", they are caught by Nazi soldiers and returned to the school.

On Parent's Day, Julien's mother arrives and takes him, his older brother (Francois), and Jean (at Julien's request) out to lunch. The hard times become more apparent when Mrs. Quentin attempts to order fish but the only option available is a rabbit and margarine dish. She also speaks of her husband's failing business, her daughter's work in the Red Cross, and the frequent bombings of Paris. During their meal, two French policemen enter the resaturant and attempt to expell a wealthy Jewish patron. The situaion becomes strained when Francois calls them collaborators and the rest of the diners voice their opinions and discontent loudly. A group of German soldiers also eating at the restaurant ask the French policemen to leave and allow the Jewish man to stay supposedly to impress Mrs. Quentin.

Julien waving goodbye to Jean
After the parents have left, Joseph, the kitchen boy, is caught stealing the school's food supplies to sell on the black market. He is fired though Julien, his brother, and several other boys contributed by trading their personal food items from home. Father Jean (the monk who runs the school) punishes the boys but cannot send them home because of their parents. Joseph is forced to leave the school and, to find a job, joins the Nazis.

During Algebra one day, a man of the Gestapo and two soldiers enter looking for Jean Kippelstein on a tip from the embittered Joseph. Julien glances back at his friend and gives him away so Jean is forced to leave with the Nazis. The other two boys who were hiding at the school were also found and taken away with him to Auschwitz where they all died. Father Jean was arrested for his crimes and died in a camp shortly after liberation.