When the plot of Pentiment switches from abbey drama to murder, Andreas is presented with multiple suspects to investigate. Some involve questioning the people of Tanning while others involve snooping around the church. Earlier in the game, Mother Cecilia behaved strangely around the victim, drawing some of Andreas' attention. If players wish to investigate the sisters of the church and save Brother Piero, they'll have to focus on The Baron And The Nun quest.
Spoilers for the first Act of Pentiment.
This quest involves past sexual harassment and assault.
The investigation won't begin until Baron Lorenz Rothvogel is murdered in the chapter house, as seen in Pentiment's preview. Although afterward, Brother Florian will push for Andreas to visit the Druckers for a meal, players can go speak to Mother Cecilia in the prioress's house. Players don't have to rush this interaction, though, as she will appear a few different times over the next few days. When asking her about the murder and her behavior, Andreas must be honest, upfront, yet kind. There's no use in beating around the bush about what the player wants to know, but Andreas must come across as wanting to help Brother Piero. If he does, Mother Cecilia will mention the baron's previous interaction with a nun, implied to be an assault.
Investigating the Nuns in Pentiment
After speaking with Mother Cecilia and eating with the Druckers, investigate the herb hut to the right of the convent. Although a small detail, the historical detail in the convent's design, alongside everything else, is one of the joys of the game Andreas will find a bloody shovel frequently used by Sister Matilda. If Andreas visited Brother Florian for the autopsy (recommended for any playthrough), players will know the Baron's CoD was a blow to the back of the head with a blunt object hard enough to crack the skull, and a shovel would fit that description. When the player speaks to Sister Matilda about the shovel, she will claim she was killing baby rabbits in the garden and show off a mysterious letter.
At this point in Pentiment, Andreas will want to check the abbey records, but they are in the library, which he is forbidden to access. Players may have already found the secret door to the library if they spent time exploring the church. Head into the crypt and investigate the picture of the Virgin Mary and baby Jesus. A door to the library opens up upon messing with the key. As the nuns are likely still working at this time, players must wait until Compline, a.k.a night, to sneak in.
When Compline falls, Andreas should return to the church and sneak through the secret door in Pentiment. There are lots of records to search through and plenty of information to gather about the nuns. The key clue is upstairs, and discusses Sister Matilda spending some months at a hermitage after Baron Rothvogel visited the abbey. After a few mishaps, including Andreas witnessing a forbidden gay relationship between two monks, he can speak with Mother Cecilia. Bringing this up to her in the same manner as the first discussion will reveal the truth. The baron made advances on Sister Matilda, and when she refused, he beat her. Her stay at the hermitage was both for recovery and to avoid scandal falling on the church.
At this point, players have all the evidence they need for the archdeacon's visit, if they wish to accuse Sister Matilda of killing Baron Rothvogel. However, Andreas' decision will never be confirmed as right or wrong, and players are more than welcome to accuse someone solely because their death would better the community. As Pentiment's name suggests, there are flaws and layers to every case, and the story of The Baron and the Nun may be the one that players settle on.