Petrus is the Queen of Attolia's physician, as appearing in the third book after an assasination attempt on the King. Attolia mentions that he has served as her personal physician for a number of years and he operates a charitable hospital operation with the crown's funds, where he conducts experiments to treat ailing patients.
He appears in The King of Attolia after the king is wounded during after a failed assassination attempt. While trying to bandage and apply medication to the king's wounds, his attempts to stitch the wound together is made impossible by the king's resistance. Petrus is able to get most of his stitching work done until the queen faints, causing the king to "erupt like a wild animal caught in a snare" when someone shouts in alarm. His work is nearly undone until the Eddisian Ambassador calms the king down, who behaves more cooperatively in response to the queen's fainting spell. A fearful and nervous but honourable man by nature, he later approaches the king and queen when he discovers quinalums mixed in with the king's lethium, which could have potentially poisoned and killed the king.
He does not appear in A Conspiracy of Kings, but is mentioned by Eugenides as having gotten into an argument with Eddis's royal physician, Galen, over in regards to their professional ability as physicians over how to treat the king's health.
- "Oh, no,Your Majesty, no, as you can see, it is a very fine needle"
- "Its a mixture of aqua vitae and v-vital herbs"
- "My Stitches! My Stitches!"