On this page of our guide to GreedFall, you will find a walkthrough for the next main mission - Battle of Red Spears.
You have to reach a location called Vedrad "The Red Woods" and reach Vedrhais village. Talk to Arwant, and you will be directed to the battlefield. Go there - you have to defeat a bunch of enemies and try to save Siora's sister, Eseld.
Speak with Eseld after the battle. You can use intuition/charisma to convince her to stop her revenge. The game will now display a time counter - you have to find the wounded on the battlefield and try to help them.
Walk around the battlefield and wait until Siora says that she sees a wounded. That person will be marked on the map - go to the wounded and heal him. During the search, you will see a cut-scene during which Siora attacks a wounded soldier. You can convince her to take revenge or tell her to stop. For the treatment of wounded, you will receive +2 points to the Islanders reputation and 1,400 XP.
During the search, you will come across ruins - explore them and you will come across a big painting. You will also get a companion quest for Siora - Find the Bladnid Queen.