By a cold day of September of 1872, two young brothers named André and Julien Volden leave Phalsbourg in Lorraine to grant their recently deceased father's wish. Their goal is to see their uncle Frantz in Marseille. Their first stop is at père Étienne's, an old friend of their father's. Then they leave to Saint Quirin to find Fritz, the forest warden. Unfortunately, Fritz, who is supposed to help them cross the German border, has just broken a leg. Though he sets up a plan for them to reach Celle where a farmer helps them to reach Epinal with a note for old cousin Gertrude at whose place they will live for a month. During that time, André works for a locksmith and Julien goes to school. The kids finally leave for Vesoul, then Besançon. Thanks to a nice hotel owner in Vesoul, our heroes continue their journey with Mr. Gertal, a door-to-door salesman. They cross the pass of the Faucille and buy cheese at the Rousset and stop to rest a few days in Bourg-en-Bresse. They get a horse named Pierrot to take them to le Creusot and Moulins. In Thiers, they have to face a fire that ravages the farm of Mr. Gertal's friends. Thanks to André's courage, no one is hurt. André and Julien part ways with Mr. Gertal in Valence. They ride a train for the rest of the journey to Marseille where they find père Jérôme who tells them uncle Frantz has left the city and has given no address. The two brothers find a sailor in Cette who knows the whereabouts of Frantz. He is in a hospital in Bordeaux. The sailor takes them there through the Canal du Midi on his boat, "Le Perpignan". André and Julien want to bring their uncle back to Phalsbourg by boat on the "Poitou" but a storms hits them by Cherbourg and they barely survive. They are saved by a cargo headed for Dunkerque and finally reach their destination.