Pavel, nicknamed Pious for his priest training, was a bandit leader, but after taking part in the Neuhof massacre, he went to the Sasau Monastery to take his vows and become a monk, becoming known as "Brother Antonius".
At some point, Pious was training to become a priest, but instead became a bandit leader, with his gang consisting of Reeky of Ledetchko, Timmy and Limpy Lubosh. They were hired to take part in what they thought was a robbery at the Neuhof stud farm, but once the attack began, they were horrified when Runt and his gang began to slaughter the horses, and even the people, including Smil. Henry would later investigate the massacre in The Hunt Begins, which would lead him to unravel a massive conspiracy that threatened everyone in Sasau.
After the massacre, Pious had an epiphany, realizing "his life is worth shit", and decided to repent for his sins. To this end, he went to the Sasau Monastery and took the vows as Novice Antonius, along with Novice Lucas, Novice Siskin, and Novice Jodok.
Meanwhile, Henry is given a test by the bandit Kozliek in order to prove he was worthy of joining their gang - kill Pious. To this end, he begins A Needle in a Haystack, where he infiltrates the monastery to find the former bandit. Henry manages to infiltrate the monastic order by posing as a novice, and speak to Antonius, who tells Henry that he's there for the books and education.
At first, Brother Antonius is friendly with 'Brother Gregor', telling him a cover story that he grew up in Vlaschim, but decided not to follow his father's profession and become a merchant. During Nasty Habits, Henry would discover that the circators have been sneaking down to the cellars to drink, which is against Monastic rules, and Antonius would advise him that interfering in the senior monks' business would not end well.
During The Abbot's List, Henry learns that the Abbot has been making discrete inquiries into Antonius's backstory, and evidently does not believe his tale. Not only that, but as part of The Trials of a Novice, Lucas will confide that he knows Antonius' backstory is a lie. The final nail in the coffin is a dagger that Henry finds in Antonius's chest.
It soon becomes obvious to Henry who Pious truly is, and he confronts him. If he does not arrest or murder him straight away, Pious attempts to poison Henry's food. However, he survives, and a repentant Pious will offer to collaborate. Henry can either agree to the deception, kill one of the other novices and pretend it was Pious, or just kill Pious. If he lives, Pious escapes from the Sasau region, promising to never return.
If you've talked to Sir Radzig, you can arrest Pious after helping him get out of the Monastery. He will initiate a fist fight with you, and when you win, you will take him to the Bailiff in Rattay. However, you won't be able to get Pious' dice this way. Fortunately, there is a little trick you can do to arrest Pious, AND still get the dice from him without killing him. After he is taken to the Rattay jail, lockpick his jail cell door. If there's a guard sitting on the bench directly behind you, continue lockpicking the door, as he does not care if you break into Pious' jail cell. After you break in, close the door behind you and DO NOT silently knock him out. This will end up killing him for some reason. Instead, punch him once or twice. He will then get knocked out and you will be able to loot his body for both the dice and his groschen. The guard will rush into the room, where you can then pass a speech check or bribe him in order to stay a free man. Pious will then regain consciousness in 30 minutes, and you will have successfully gotten Pious' dice without killing him nor letting him escape a free man.