3:4 Blood Trials

Blood Trials

Pure Blood
Use Ope's help to find  a stable strain if the virus
Very Hard
8500 XP

Complete all the available sidequests first if you want before heading to Ope's Cave and do this main quest. Once ready, fast travel there and talk to Ope. Escort him back to Mowen's Boat. Once he reaches the boat, make all the necessary preparations and travel with him to the catacombs.

Once you've landed on another uncharted territory, stick close to Ope and protect him from any undead. You'll eventually reach a village where there are tons of these. The stupid shaman will draw attention by moving in the middle of the village. Just be prepared to fend off the attacks.

Follow him as he leads you deeper into the woods. He'll stop and warn you about incoming enemies. Brace yourself for an infected ambush.

Once they're taken care of, continue along the path and get rid of more walkers and a thug. Pick up some fruits along the way as needed, then continue to the hanging bridges. A butcher and a couple of infected will ambush you so get ready.

Continue following him until you reach a drawbridge. You need to operate the lever on the other side so jump to the other side and operate the lever. Continue following Ope until a cutscene plays.

After the scene, you'll have to protect Yerema this time. Stick close and escort her as she leads you out of this place. You don't need to fight all of them; just follow Yerema and kill everything that attempts to slow her down – especially the infected. Continue running and heal as necessary. Once you're near the boat, a scene will trigger. You can rush to Mowen's aid immediately then deal with the remaining zombies along the way.

Ancestral Recall

Continue escorting Yerema until she reaches the boat. Finally, travel back to the Laboratory once done. You'll have to escort her again on foot until she reaches Dr. West. There will be a lot of zombies along the way so make sure you get rid of them quick. You'll finally reach the vicinity of the lab but then again, you must kill every threat before Yerema can move.

IMPORTANT NOTE: There's a known glitch at this part where Yerema will refuse to follow you even if you killed all the zombies in the area. According to what I've found in the forums, this happens if you quickly killed the zombies above the stairs in the catwalk to the right before the game tags them as important targets. To prevent this from happening, let the “key” zombies rise up and turn to red skulls (target objectives) before killing them. Take note that they will stand up one by one once you get near them. Upon killing the third zombie, Yerema should move from her position and start running ahead of you. If reloading your checkpoint doesn't bring them back, quit the game and reload your game save.

There are several infected here and a few walkers as well but you can exploit them by closing the gate and attacking them from behind it, preferably with a firearm so you can aim and land easy headshots. After clearing the area, Yerema should run by herself to the lab and talk to Dr. West to complete the quest.