You remember soldiers, Jane and Payne, for sure. They guard the checkpoint, the border between relatively safe southern areas and the most dangerous city zones. One of the soldiers’ groups headed deeper into the northern lands and lost connection with their chiefs. The group had to settle there and set up a camp. Most of them didn’t endure the lack of food and water, and the group also lost a lot of people due to the surrounding enemies. You need to meet with one of the characters in the middle of the military camp and help him.
The task chain will lead you to the second new area, the burning plane. It appears for 3 days only after you accept the Major Jax quest.