His Old Self

 is a side quest in.

Synopsis
Kaenra is a woman recovering from a rather bad experience with her fiancé, Purnisc. He started bringing svef addicts into their home and pushing drugs. When she confronted him about it, she received a fist to the nose and an order to get out. She asks the Watcher to return the betrothal ring Purnisc gave to her, as it once belonged to his grandmother.

Overview

 * 1) Talk to Kaenra in The Goose and Fox in Copperlane.
 * 2) Talk to "Purnisc" (Nyrid) on the first floor of Purnisc's House in Copperlane.
 * 3) Talk to the real Purnisc on the second floor. [optional]
 * 4) Expose Nyrid.
 * 5) Deal with Purnisc.
 * 6) Report back to Kaenra.

Walkthrough

 * 1) Find Kaenra at a table in the back of the Goose and Fox tavern in the Copperlane district of Defiance Bay. She will tell you about her fiancee Purnisc who has started to act strangely and cut off contact with her, and ask you to return his grandmother's ring to him, a token of engagement.
 * 2) Exit the tavern and find Purnisc's House to the north-west in the same district. Enter, and speak with "Purnisc" in the first room to the right. If you give him the ring, he won't seem to realize who Kaenra is. Something is clearly not right, so you must investigate further. You have two options:
 * 3) Provoke a fight: If you select the passionate response after giving him the ring, or you simply attack him, a fight breaks out and "Purnisc" reveals himself as a wizard called Nyrid! When he's almost dead, he will ask for mercy and you can choose to take him prisoner (provided you have already restored your stronghold dungeons) or finish him off. You can then either proceed to the second floor to find the real Purnisc [→ 3], or end the quest prematurely by returning to Kaenra and telling her the ring is delivered. (She will give you Unwavering Resolve and Minor Positive reputation with Defiance Bay.)
 * 4) Proceed to the second floor without bloodshed: If you don't want to fight (just yet), talk instead to the Mercenary in the kitchen who is guarding the stairs to the second floor. To get through, you must bribe him (100 ) or intimidate him (Resolve 14+) [→ 3]. Note: If you try to get past him a second time he will attack you. If there are other mercenaries on sight they will join the fight.
 * 5) In any case, once upstairs, make your way to the room on the right either by fighting (you can loot the door key from the mercenaries' bodies), or by sneaking (you'll need a character with Mechanics 5 for the door).
 * 6) Inside you'll see the real Purnisc lying on the floor. He will ask you to kill Nyrid, the mage who is impersonating him downstairs.
 * 7) Unless you have already fought Nyrid earlier, go down and confront him. This conversation leads to two options:
 * 8) Make a deal with Nyrid: He will lower the price of Svef to 68 if you kill Purnisc for him. If you do this, the quest ends, and Kaenra vanishes from the tavern, making you unable to get a reward from her.
 * 9) Fight Nyrid: When he's almost dead, he will ask for mercy and you can choose to take him prisoner (provided you have already restored your stronghold dungeons) or finish him off [→ 6].
 * 10) Once Nyrid is gone, talk to Purnics again. He will ask you to talk Kaenra into returning home and also to keep his svef dealing a secret. If you agree to this (or force him to give you a discount with Might 14), he will then sell Svef to you at 68 next time you enter his house. You could also kill him. Ultimately you can even refuse to do him another favor, which ends the quest prematurely and results in him immediately trading with Svef again, even if he is not yet back in full form.
 * 11) Finally return to Kaenra. If you're being honest with her then pick the Benevolent or Passionate answer you get a slight increase with reputation with Defiance Bay twice. Whatever dialog option you pick with her, she gives you the amulet Unwavering Resolve - except if you killed Purnisc after killing Nyrid and admit to it, in which case she will be shocked and appalled.