Start the mission here
[7,-59]Take the quest with the Great Jarl Ordyn at [7,-59].
Take the quest with the Great Jarl Ordyn at [7,-59].
Talk to Great Jarl Ordyn. He will send you to the Jarl's Mariner, which can take you to Belladonna's island.

At the dungeon entrance, talk to Ayin Spyr. Then complete the Dungeon of Belladonna.

Defeat Belladonna at the end of the dungeon. After the fight, talk to the NPCs that appear in the room to validate the progress.
Belladonna
Return to Great Jarl Ordyn to announce victory. Then enter the tavern on the left and talk to Ayin Spyr to close the mission.