Before going missing, Mirisa was in a relationship with Jeleen.
Mirisa set out on a mission to teach the warriors of Thirsk about the Imperial Cult and how drinking mead is a sin. Erich the Unworthy was angered by this statement and in his rage he knocked her unconscious. She then awoke in his chambers, which by the time the Nerevarine reaches her, was over three weeks ago.
Since that time she said Erich would come taunt and beat her everyday, and all she was given to eat and drink was mead.
Speaking to Jeleen about Mirisa will activate this quest. He will send the Nerevarine to Thirsk in the northern area of Solstheim in search for her. Asking most members about Mirisa will have direct them to Erich. Erich will act as though he knows nothing when spoken too.
Mirisa is upstairs behind a level 50 locked door. Erich carries the key to this door which can pickpocketed from him or looted off his corpse.
Upon rescuing her she will need to be guided back to Fort Frostmoth. It should be noted that she will attack any enemy in sight and is quite weak, often resulting in her being killed.
If she is returned alive, she and Jeleen will be reunited. She can then become a merchant and buys potions and ingredients
If she is rescued but killed before reaching Fort Frostmoth, there will still be a reward though Jeleen will commit suicide in his grief.