Hugues d'Avène, a dignitary in the Order of Hospitallers, inspects the commandership. Thomas and Géraud, who are embezzling part of the "taxes", are afraid they'll be discovered. Plus, Thomas thinks he recognises a lover from his youth in Constance de Montet, a young manor owner returning to a neighbouring domain...

The commander, Roger de Neuville, defends Géraud. Thomas, who uncovers the real mission of Hugues d'Avène, offers to help him in his quest for the Templar's treasure in exchange for his freedom. Meanwhile, daily life at the Commanderie continues...

A woman from the village arrives at the Commanderie with a dead infant who was not baptised. Friar Pons is convinced that the child was killed. At the same time, despite the "diabolical" threats levied against them, Hugues and Thomas continue the search that will lead them to the treasure.

During a procession, some villagers are subject to violence at the hands of Le Breton and his gang. Géraud decides to assist them. Because he comes a bit too close to the truth, Hugues d'Avène is assassinated...

The burial of Hugues d'Avène is interrupted by the arrival of the Duke of Anjou, who demands that his friend's murderer be brought to him. While this is happening, Géraud convinces a farmer, Paziol, to leave the bishopric's land to live at the Commanderie, which is short on hands...

Determined to relieve Constance of a dangerous mission, Thomas helps the Duke of Anjou find the treasure. A certain Mathieu arrives at the Commanderie claiming to be married to one of the laundry maids, but no one recognises him, not even his wife Catherine, who has remarried a wealthy farmer..

Géraud is irresistibly attracted to a young sculptor hired at the Commanderie. To avoid giving in to this mortal sin, he avoids the young man and martyrs his body and spirit. Thomas and Elias discover the treasure's location and are preparing to open the chests when Constance interrupts them...

Géraud, crazed with love for Laurent, the young sculptor, commits what he feels is the most horrible of sins. Constance agrees to lead Anjou and his entourage to the crypt where the treasure awaits. Unless it is just another trick..