Once you get inside, they show you the letter that was sent to them by the cleric Joseph in Hertoplowis. It reads:
I have found the location where they are holding Emmerick. He was taken into custody first at the constables’ prison. It would have been easier to get him from there, but I didn’t know in time to tell you. They have so many procedures and regulations here, its Grean. He was moved after two weeks, I think he had been roughed up some. I followed, but they eventually used magic I couldn’t keep up with to get where they were going. It took lots of coin, but I found his new prison. It is a place called Yorbone, a holy site for the Eternal. It is a small fortress. It is in north central Hertoplowis. Follow the dead and you will find it. Don’t contact me via magic. The Regulators and Judges are closing in on me. If I am near when you arrive, I will come with you, otherwise, after a month; I’ll make my way back home. Good Luck.
Joseph