Osen is sympathetic to Sonea, even after she is outcast to Sachaka. He offers her a few chances to change her mind, and helps her to get on her horse.
During the Ichani Invasion, Osen is paired with Lorlen. After they had expelled almost all their magic, they attack a weak Ichani who was after them, killing him. They take refuge in a nearby building, however Kariko blasts the side and Lorlen pushed Osen out of the way. Osen managed to escape the falling debris, but Lorlen didn't. He calls for help which is answered by Dannyl and Farand, and they start digging him out by hand.
After the death of Lorlen, Osen becomes Administrator, now using Lorlen's old office as his own. However, he rearranges the room so it does not remind him of his predecessor. Osen makes a blood ring so he can communicate with Dannyl while in Sachaka.
Both Osen and Balkan order Sonea and Kallen to investigate Lord Leiden's murder. When Dannyl is researching information for his book in Duna, he finds out that a gemstone that could manipulate the thoughts of the user, preventing an effective mind read. This information helps with the trial and after a second mind read, finds Naki guilty. Osen orders Kallen to execute her.