Its plot is set in France during the 14th century, around Avignon and Carprentras, and uses as background the feud between the Rome and Avignon Papacys
. It is centered on two main characters: the Inquisitor Guillermo Barnal (real name Guillaume of Tasteville) and the Jewish doctor Samuel of Napoli. The former investigates on a plot against Avignon Papacy, the latter makes researches about the plague; Samuel soon becomes a suspect for Guillermo.
Other relatively important characters are :
- David of Napoli, father of Samuel and doctor himself
- Aurore, daughter of Samuel
- Madeleine, the witch
- La Plotte, bishop of Carpentras
- Silas, novice monk of Guillermo
- Blaise Duterte, a midget who catches rats and occasionally sells some to Samuel and David
- Jacob of Millaud, the Great Rabbi of Carpentras
- Nathanael Arnavi, another rabbi of Carpentras
- Eleonore, a actor in the plot from the Rome Papacy
- Raymond of Turenne, ruler of Carpentras
- The antipope Clement VII
- Catherine of Siena, ambassador of the Rome Papacy
- Pierre de Luxembourg
Inquisitio provides examples of:
- Armor-Piercing Question : from Samuel/Nicolas to his brother Guillaume: "Why did you leave me?" Barnal promptly and completely breaks down.
- Artistic License – History:
Word of God says that it is totally intentional. - The Atoner: Guillaume, who is persuaded that the plague which killed his family has been caused by his sins.
- The Black Death: The series open with the Tasteville family (Guillaume Barnal's relatives) — and the surrounding village — decimated by an outbreak of plague. Catherine of Siena's goal is to trigger an outbreak in Carpentras in order to "prove" the Pope in Avignon is an imposter.
- Chronic Backstabbing Disorder: Raimond of Turenne.
- Decadent Court: The Avignon Papacy is depicted as one.
- Death by Childbirth: Happened to Aurore's mother, Samuel's wife.
- Dirty Old Monk: Or rather Dirty Old Pope and Dirty Old Bishops.
- The Dung Ages
- Heroic Sacrifice: David proves his innocence in the disappearance of the clerics by trial by ordeal. By jumping in the river from the bridge and drowning, he proves that he doesn't float and thus is not a sorcerer.
- Even Evil Has Standards : Raymond of Turenne is seriously creeped out when Catherine of Siena announces her intention to spread the plague in Carpentras. YMMV about Guillaume being evil, but he has his moments as well.
- Eye Scream: After believing his sins caused the outbreak of plague and the death of his family, the young Guillaume of Tasteville pops one of his eye with a shard of stained glass (showing the eye of a saint).
- Eyepatch of Power: Guillaume Barnal wears one.
- Gory Discretion Shot : When Guillaume prepares to pluck his eye out, the camera only shows his back, and when he does the actual deed, we only hear his screams off-screen.
- Historical Domain Character: Antipope Clement VII and Pierre de Luxembourg.
- Historical Villain Upgrade: The main villains of the show are Catherine of Siena and Raymond of Turenne.
- Historical Villain Upgrade: The main villains of the show are Catherine of Siena
- Honey Trap: Eleonore has this role under orders of Catherine of Siena. Several times.
- Hot Witch: Madeleine.
- I Have No Son!: The great rabbi Jacob didn't like Samuel since the death of his daughter — Jacob is the father of Samuel's wife — but he remained courteous. Then, when the fact that Samuel wasn't born Jewish but the lost brother of Guillaume began to be known, at one instance Jacob goes "I have no grand-daughter" on Aurore.
- Identity Amnesia: Nicolas of Tasteville lost all memories when he caught the plague during his childhood. It led him to believe he is Samuel of Napoli, the son of the Jewish doctor who adopted him.
- Jack Bauer Interrogation Technique: This is a series about medieval Inquisition, it had to be expected...
- The Late Middle Ages: Except the beginning of the first episode (which happen 25 years before the rest of the show), everything happens in 1378.
- Light Is Not Good : Catherine of Siena and Eleonore del Monte only wear light or white clothes. The first is the main villain of the series, and the second is her accomplice.
- Long-Lost Relative: Samuel is Nicolas, the younger brother of Guillaume. Contrary to what everyone thought (including Guillermo), Nicolas didn't die from the plague, but has been found in a mass grave still alive, and adopted by David. Nicolas then sincerely believed to be Jewish like David, to all appearances his father.
- Malevolent Masked Men: The plotters wearing plague doctors masks.
- Ominous Latin Chanting: The opening credits.
- Seers: Aurore.
- Shout-Out: It isn't the first fiction about a monk belonging to the Inquisition and his novice investigating suspicious deaths and disappearances of clerics. Made even more blatant with the character's name, "Guillaume of Tasteville", which sounds oddly close to "Guillaume of Baskerville".
- Shroud of Turin
- Trailers Always Spoil: Technically not a trailer, but the summaries for the show in some French television magazines featured a subtle spoiler. The beginning of the plot of the series was very quickly summed up, but the character of Samuel was called "Nicolas", which spoiled a bit The Reveal of Samuel being Guillaume long lost brother.
- "Where Are They Now?" Epilogue
- You Have Outlived Your Usefulness: hilariously averted by Turenne who doesn't kill Blaise after he talked, but instead lets him go because "You can't kill everybody".
- Younger Than They Look:
- Catherine of Siena is played by an actress who is 44 or 45 years old; the character was 31 years old in 1378.
- Pierre de Luxembourg was 9 years old in 1378, but he appears as an adult in the series.
