This quest becomes available after you complete The Huntress. As you walk by the Hunter’s Hut, Petra will approach you asking if you’ve seen her brother, Wallace, who hasn’t returned to camp as he normally would. You can choose to help her find him now, or you can postpone the quest for another time if you wish.
Once you accept to help Petra search for Wallace, she’ll mention a crossroads to the northeast, where Wallace sometimes sets up camp when he’s travelling back from Medeshamstede Abbey. Head northeast with Petra to look for the potential camp. As you approach the area, Eivor will note the ruins of a Temple of Pluto.
When you reach the ruins, Petra will point out the remains of a small camp. Examine the the area to identify a set of tools. Petra points out the entrance to an area beneath the temple, where Wallace might be found. When you reach the bottom of the steps, a wild boar will attack you. Kill the boar and then inspect the clues in the form of Wallace’s clothes, a knife, and a cooking pot. As you inspect the clues your vision will begin to distort.
After you’ve inspected the clothes, knife, and cooking pot, Petra will call for you to follow her upstairs. She swears that she has seen the same white elk which led her to Wallace when she first found him, and will quickly run westward. Don’t worry if she outpaces you: she will stop at a small house nearby. When you enter the house you will encounter a strange scene in the form of a group of strangers apparently having a good time.
After noting the strangers in the house, Petra will call for you outside. When you approach her location a lightning strike will hit and she disappears. Continue west until you see the white elk in the water. Speak with the elk and then follow it through the woods. Eventually he will vanish, and a number of enemies will appear. Defend yourself against them until Petra wakes you from the strange vision.
Follow Petra and walk in a straight line when she asks you to. After falling from the sky, you will need to follow her west to the same area where you helped her kill the wolf pack during The Huntress. At this point the wolf spirits will attack you, kill them as quickly as possible or until the vision fades, at which point you’ll encounter the white elk again. Follow it to the cliff edge in the south to begin a cutscene, at the end of which the quest will complete.