Sergeant Chesterfield and Corporal Blutch arrive in their new assignment where the general desperately seeks volunteers for a perilous mission. Alighted by the fifteen hundred dollars of bounty, our two acolytes sign without thinking. Their mission is simple: to infiltrate the Southerners and destroy railway tracks, ammunition depots, bridges, cotton harvests in order to weaken the enemy. To do this, two Mexican mercenaries, José and Pedro, who know this region perfectly, will accompany them in this expedition...