It appears that Erend's sister Ersa was kidnapped instead of slain, but many questions remain. Where is she? Who is responsible? And why?
After realizing that Ersa may still be alive, fast travel back to Meridian and enter the Palace of the Sun to meet up with Erend.
Upon reaching the entrance to the Palace, speak to Marad and he will grant you entrance to the Palace. Follow him all the way to the Sun King for a conversation.
The Sun King has requested for Aloy to see this search for Ersa through. Head for Pitchcliff and meet up with Marad's operative.
Marad's Operative is missing and Aloy must find him. Scan Pitchcliff for any tracks and follow them. You'll find Marad's operative dead but has drawn a map for you to follow.
When you reach Dervahl's Camp, a cut-scene will start and now you must kill the Outlanders and Machines.
You can unchain the machines and override them should you have the need to get clever. They will fight for you against the other machines and outlanders.
You'll have to find Ersa inside the workshop after clearing the area of machines and outlanders but you'll also have to defeat Dervahl's champion to go inside the workshop. Defeat his champion and loot his body.
Go inside the workshop and disable the sonic barrier. Continue forward and you'll start a cut-scene with Ersa on the brink of death.
Investigate the workshop for any information on Dervahl and the quest will have been completed.
