While Siorac returns to battle without having reconciled with Isabelle, the castle of Mespech is threatened by Fontenac, allied with bandits from beyond the Pyrenees. Isabelle and Sauveterre join forces and organize the defense of the estate, while Pierre gets closer to his brother Samson, digging the gap with François.

After a heroic resistance led by Isabelle, Mespech triumphs over the bandits, revealing Fontenac's betrayal. Returning from the war covered in glory, Siorac, now Baron of Mespech, takes the opportunity to announce the community's conversion to Protestantism, despite the intractable opposition of Isabelle, faithful to her Catholic faith.

After their conversion, Siorac and Sauveterre yearn for peace, despite the resistance of Isabelle and the other women of the house. Outside the castle, the country is torn apart. Taken hostage by a fanatical Protestant leader, Isabelle is saved in extremis by Siorac. The couple reconcile, Isabelle is pregnant again.