Francois arrives at the Fort of Casal, under siege by the Spanish, to volunteer but is dismayed by the cool reception by Thoiras, the French commander. Don Alonso vows to prevent the French ambassador from attending a peace conference.
Disobeying a direct order not to raid the Spanish for supplies, Francois is arrested for subordination. The court-martial tribunal orders his execution but Thoiras offers him a more honourable death, a dangerous mission through enemy lines.
Francois and Guillot escape the fort disguised as lepers but Ricardo in the Spanish garrison is not easily fooled. Betrayed by the woodsman, they hitch a ride with Mazerin and Bodernelli, papal representatives for the peace conference.
Mazarin gives Francois his carriage to escape Ricardo and his troops, but they are soon captured by bandits who also have the Duke De Sospel and his daughter. Don Alonso gives Mazerin news of the Duke's capture.
Francois escapes with Isobelle but Guillot is picked up by the Spanish with the Duke and arrested. On her return, Isobelle clashes with Don Alonso over the arrest of his prisoner. Francois is thwarted in meeting with his next contact.
While waiting for instructions from a contact, Francois joins a troupe of actors. While Don Alonso suspect Mazarin of helping him to escape, Mirielle informs a worried Isobelle that Francois has not been caught.
Ricci hides amongst a theatrical troupe while Mireille arranges for his escape from Navarre to join the French troops on the border. Ricci gratefully thanks the traveling players for their assistance and gives Zerbinette a farewell kiss, which Isabelle sees and misinterprets. Filled with jealousy, Isabelle informs the Spanish troops where Ricci is hiding.
Acting on information supplied by the jealous Isobel, Ricardo's men pursue Recci to the top of a cliff where he apparently falls to his death. The peace conference sponsored by the Pope gets off to a rocky start owing to the absence of the French delegate. Mazarin's letter to the delegate is destroyed by Ricardo, but the torn up pieces are discovered and returned to the Papal envoy who accuses Alonzo of complicity.
Mazarin's second message to the peace conference's French representative is delayed when Spanish cavalry steal the emissary's horses. Isobel is stricken with remorse over causing Recci's death and determines to become a nun. Recci survived his fall, however, and flees the attacking Spanish while Mirelle and her men fight a desperate rear guard action.
While fleeing the Spanish cavalry, Recci and Guillot chance upon Bodinelli who has been thwarted in his efforts to deliver Mazarin's message to the French ambassador. Recci agrees to break through the Spanish lines and deliver the message to the marshal. Meanwhile Mirelle listens to her gallows being built outside her window and Mazarin plays for time.
Mazarin and the peace commissioners hammer out a treaty to end the armed conflict between France and Spain, but Don Alonzo conspires to prevent word of the treaty from reaching Casal until Castellan and his forces can capture the French fort.
Recci returns from Casal only to learn that Isobel has taken her vows as a nun and joined a convent. Despairing, he takes Guillot and travels to the Holy Land as a soldier of fortune. Eventually the knights errant return to France and are greeted by their old comrades in arms who worked together to save the French fort from capture - including one friend whom they never expected to see again.