August 1914. While the German army is gaining ground in the North of France, four boys aged 10 to 15, LUcien, LUcas, LUigi and LUdwig are left behind during the evacuation of their orphanage. Without the protection of Abbé Turpin and the schoolteacher Leutellier, the Lulus are now stranded on their own behind the enemy front line. Soon joined by LUce, a pretty young girl separated from her parents, they decide to reach the neutral country of Switzerland by all means possible... they embark on an adventure for which nothing and no one has prepared them!

Back to school for Ducobu, Léonie Gratin and Latouche. But this year, a major rival for Ducobu arrives at school: TGV, the king of cheating 3.0. While the financial situation of Saint-Potache becomes disastrous, the two dunces will have to unite their creativity to win a song contest and save their school.