The Phylactery's Promise

 is a side quest in.

This quest can be started when you have completed both, the Siege of Crägholdt and The Iron Flail. A dead assassin shows up in Stalwart, just west of Hamond's Emporium. Reading her soul enables access to a marshy area called Mowrghek Îen.

Synopsis
Taking Concelhaut down puts the Watcher in the sights of another powerful archmage. Confrontation is only a matter of time.

Walkthrough

 * Once in Mowrghek Îen, you must fight through a village of cultists in order to confront their leader, who turns out to be a powerful wizard; the archmage Llengrath.
 * The player has two options: fight Llengrath, her flunkies, and her two Bog Dragons, or cut a deal with her.

Coming to an agreement
Dealing with Llengrath peacefully requires that you teach her something, or to convince her that you can keep the secrets of the phylactery. This is an involved conversation with a fair amount of checks and branches. Assuming you don't attack her outright, the decision making starts when Llengrath says "In truth I am glad you came. It saves me the effort of chasing you.", and ends when she says "...But perhaps there is a way."


 * If you don't have Concelhaut's Skull on you, your options are limited to:
 * "Wait! At least help me understand." then "We're both arcane practicioners. I appreciate what you've accomplished here. Can't we talk about this?" - Requires that the Watcher is a Wizard, jumps to the options under the Intellect 16 check below.


 * If you do have Concelhaut's Skull, say "What if I just give you the phylactery?"
 * "We're both arcane practicioners..." - Requires that the Watcher is a Wizard, jumps to the options under the Intellect 16 check below.
 * "I'm trying to keep things civil."
 * "I believe we have much to teach one another." - Requires Intellect 16
 * "You're right. Nobody should have Concelhaut's power.", then "Llengrath had the right idea." for a pass without any further checks.
 * "I saw what Od Nua did to preserve his son's life. This secret should stay hidden." - Only if you completed The Master Below,
 * "I'm a Watcher. There must be something I can teach you." - Requires one of the following conditions to convince her:
 * Have earned the favour of a god by completing Council of Stars or Lair of the Eyeless
 * "I have friends in high places. You might even call them divine."
 * Learned the Engwithan language from Icantha during Undying Heritage
 * "I've discovered much about the Engwithans. I could share that knowledge."
 * Resolve 17
 * ''"Then you'd be foolish to waste the opportunity."'
 * "I'm a decent caster, you know. What if you teach me?" (Watcher is a Wizard) - loops back to previous conversation
 * "How can I convince you that I'm not a threat?" (fails if you have Deceptive 3) then "What if I swear to keep the secret of the phylactery?" - Requires of the following conditions to convince her:
 * Honest 2 - "On my honor, I swear it."
 * Resolve 20 - "On my word. Nobody will ever know."
 * Stoic 2 - "I'm not really much of a talker."
 * As a Wizard - "Consider it a wizard's vow."
 * As a Priest - "Before the gods, I swear it."
 * All other options lead to a fight

Reaching a peaceful agreement rewards the Watcher with a unique talent, Mental Prowess, and adds 5 Stronghold Security.

Doing things the hard way
If the player chooses to fight, however, be prepared for a difficult battle. Llengrath herself is a powerful wizard, but the real threat comes from fighting two dragons at once.

Defeating Llengrath yields her unique grimoire (containing five spells which are otherwise unobtainable), as well as 4 Bog Dragon Scales, assorted loot, and 15 Stronghold Prestige.

The battle is significantly easier if one or more of the three powerful opponents are disabled. To that end, note the following resistances and immunities (or lack thereof, in the case of stunning).