At the temporary elven encampment (south of the Abandoned Sawmill), if you do not provoke the elves, Tovah will ask you to help rescue Saheila, who has presumably been captured by the Lone Wolves and held hostage there. If you killed Saheila back in Fort Joy at the very beginning, you get the quest Vengeance for the Fallen instead.
Tip: It is easier to build rapport with the elves if you have Sebille talk to them and choose the options that mimic their actions.
After talking to Tovah, you will need to kill Roost and then safely exfiltrate Saheila from the Sawmill back to to the elven camp to complete the quest.
Tip: If you have Ifan ben-Mezd enter the Sawmill, you'll gain immediate passage for your entire party, allowing you to freely explore first. If you don't have him in your party, you will need to have an elven character (e.g. Sebille) talk to the guards to gain passage into the sawmill.
Roost is located on the second floor of the sawmill, accompanied by two crossbowmen and two wolves. After you successfully kill Roost, all the other Lone Wolves outside will turn hostile. You will need to either kill them all or try to sneak away, although it's near impossible to do so without confrontation.
Tip: You can waypoint out of the area to immediately complete the quest after Saheila is following you.
Secret: If you use Spirit Vision, many dead spirits will appear around the sawmill, thanking you for killing them and giving you tons of experience each.
As a reward, Saheila will teach you how to master the Source (increase your maximum Source Points by one) at the camp. If Sebille is on your team, Saheila will reveal her true identity to her, and offer her the opportunity to become the heart of the Scions.