At Charlie Brown's school, Linus Van Pelt introduces to his class two French students, Babette and Jacques, who will be spending two weeks there in order to get accustomed the United States. In exchange, Charlie Brown, Linus, Peppermint Patty, Marcie, Snoopy, and Woodstock head to Europe on a student exchange plan for part of their school year. Charlie Brown is not very positive about the trip because of a letter from France that arrived before he left, inviting him to stay at a French chateau, the ChÃ¢teau du Mal Voisin (Chateau of the Bad Neighbor). The letter is written in French, but Marcie, who has been studying French, translates it.
They arrive first in London, where Snoopy leaves the group temporarily to play tennis at Wimbledon, where the beagle gets banned from the grounds when he loses his temper after losing three points. When they arrive across the English Channel in France, they pick up a troublesome rental car, which must be driven by Snoopy as none of the others have a drivers' licence.
Upon their arrival, the four go to their respective homes. Patty and Marcie go to stay at a farm, where they meet a boy named Pierre, who immediately attracts their attention. It is obvious that Marcie and Pierre have a spark between them - obvious to everyone except Patty, who manages to convince herself that Pierre likes her. Charlie Brown, Linus, and Snoopy go to the chateau, which they find is apparently abandoned, though somebody keeps leaving food for them and making their beds after they leave for school. In reality, the chateau is occupied by an unfriendly baron, and the person leaving Charlie Brown and Linus food is the baron's kindly niece, Violette.
Eventually Linus manages to track her down and demand what is going on. Violette says that although her uncle is irritable, she must remember what a US Army soldier had done for her family by helping them out in the Second World War. Violette shows Linus a picture of the soldier, and he comments that the soldier looks like Charlie Brown and it's revealed that the soldier is Charlie Brown's grandfather. They continue to investigate further, the mystery culminating in an accidental fire in the attic of the chateau, doused before too much damage occurs.
Thankful for the chateau's rescue, the baron has a change of heart and allows the gang inside, and Charlie Brown learns the truth behind the mysterious letter he received, and he, Snoopy, Linus, Patty and Marcie leave their new friends to see more of the French countryside, and eventually return home to the US.
Who are the two French students?
Babette and Jacques