This quest is only available if you didn't kill Saheila in Fort Joy.
1. Sawmill - Saheila
2. Reaper's Coast - Elves camp
If you managed to convince elves to let you to enter the ritual site then, when they complete it, you will be able to speak with them. You learn that Saheila is kidnapped by Roost and is held captive in Sawmill. If your Persuasion is high enough, you can convince the elves to leave it to you.
Your next goal is to go to Sawmill. Saheila is held captive on a floor of one of the buildings. Most of this area is heavily guarded by Roost's people. Because of that, you will have to break through by using force. The only exception is the moment, when you have Ifan ben-Mezd in your team. In such case, you will be able to freely move around the camp.
Another fight awaits at the floor. This time, you must face Roost and his personal guard which includes two wolves and crossbowmen. Staying inside of a smaller room can make this fight easier. Then, you must free Saheila. She asks you to escort her back to the Elven camp.
Speak with Saheila when you reach the camp. She will teach you how to gather an additional Source Point.
Reward: 4 guaranteed rewards + 1 from 3 that you can choose from depending on character's class