In a time when Protestants are hunted, Jean de Siorac and Jean de Sauveterre have retreated behind the ramparts of Mespech Castle. Between religious tensions with Isabelle, Siorac's wife, and the threat of a hostile neighbor, their home is in peril. As the king's investigators approach, a family secret resurfaces, upsetting the newfound tranquility.

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.