Requirements: Bring at least 9 Kinetic Siphon traps (buy these from Cephalon Simaris at a relay). I would suggest having 20 just in case.
Enemy levels: 20-35
Prerequisites: Finish main quest The War Within and complete the Mot survival level in the Void (probably the last mission you'll have access to in the game)
Reward: Harrow blueprint
This is one of the coolest quests in the game. It's the only one with a horror context. It revolves around the "god" that Red Veil fanatics worship. Lighting is turned very low during the missions in this quest. You won't be doing a lot of fighting so don't worry about leveling weapons here; just bring a powerhouse weapon to finish the mini-bosses off quickly. I would suggest moving quickly throughout these missions because the "ghost" hunting you can kill you pretty quickly and since you can't harm it you should keep a fire lit under your butt most of the time.
The first couple of missions will be mostly exploratory, figuring out what's actually going on. Then you will have a series of 3 missions where you have to use Kinetic Siphons to trap then damage "emotional fragments" of the ghost who's chasing you.
The final mission will be in the Void where you will have to use transference to break the Chains of Harrow using only your operator.
During this final mission stay invisible with
the whole time unless you're actively shooting the enemies. When you're visible the "ghost" will fire energy balls at you that can do a good chunk of damage.