you need to have first rescued Korg the orc. its in a area you get after you cross a bridge with a troll. you will need to find a certain cave to enter to go down a shafe
He's located in the same cave as Korg. (Vicoria's cave) I have no idea how to find it; sorry. Once you complete the quest, wait a day and then return to look into the cell. You'll find Vicoria messing with a new prisoner, which you can then go and talk to her about, instigating a quest to free said prisoner.