Napoleon, returning from the island of Elba, has taken power, and reconstitutes the Grand Army that is marching towards Belgium, where the battle of Waterloo will take place. Colonel Neuville is summoned by Marshal Ney. The latter entrusted him with a special mission: to meet Colonel Reynauld, a renowned royalist, who refused to hand over the command of his men to the Empire. His men must join the Grand Army imperatively. However, beyond their different policies, Neuville and Reynauld are brothers and a heavy antagonism separates them. Their duel will be all the more intense.