At 33, Clément has spent his entire life in a monastery and is about to take his final vows to become a monk. He only knows the modern world through the books and correspondence courses he took at university. Orphaned, he was adopted by the manager of the monastery and taken under his wing by Brother Benoît. When the latter is found murdered, Clément will help Elli Taleb, a totally atheist police captain, to find the murderer. Guided by this singular inspector, who raises her three sisters alone, Clément will discover the world outside the monastery and the secrets of her past.

In the Cévennes, Jonas, leader of a scout camp is found dead in a Protestant temple, a syringe in his hand. Everything suggests that it is not an overdose but a murder in disguise. To solve the investigation, Captain Elli Talleb is associated, not without surprise, with the new criminology expert in the region: Father Clément Desmoulin. Indeed, freshly graduated in psycho-criminology, Clément nevertheless remained in orders. He has extended his novitiate and sees his experiences outside the monastery as a test of his spiritual commitment. The search for the culprit of this murder will put the nerves and feelings of Elli and Clément to the test, decidedly an odd couple of investigators.

University of Montpellier. A teacher, Nathalie Josserand, 45, was found dead in an amphitheatre. First suspect for Elli: David Crosnier, 35, assistant teacher, in whose home is found the murder weapon. Nathalie's ex-companion, he has a romantic relationship with one of his students... who is none other than Maryam, Elli's sister! The relationship between Elli and Maryam (who defends David against all odds) is damaged, especially since Elli announces to her sisters that she will be forced to sell their family home... While Elise focuses on David, Clément sees another suspect, Stéphane Rocques, president of the university. He seems to have a secret that he wants to preserve at all costs.

Camino de Santiago. Eric Massol, owner of a cottage, is found on the way killed by a bullet. A priori the 6 hikers who slept at the cottage have nothing to do with this death. But Elli asks Clement to accompany them to Valmagne, Clement's monastery and the next step on the way. On the one hand, Clement walks with the group and notices some strange behavior. On the other, Elli is destabilized in her investigation by a discovery that will undermine the ideal image she had kept of her parents who had been dead for 15 years. Elli and Clément will eventually meet in Valmagne to solve a case where the culprits and victims are not who we think.

While Mathias and Clément come to deliver products from the vegetable garden of Valmagne in a restaurant in the hinterland of Montpellier, the owner of the establishment falls on the lifeless body of a second of kitchen. Elli learns that the victim died after poisoning...