Val has had confirmation that there is a slavery network in Skyrim being run by his old enemy, Aerandil, and he wants you to investigate.
"It has been confirmed that Aerandil is running a slavery operation out of Skyrim. It appears he is capturing innocent citizens under the guise of them being Talos worshipers, and selling them as slaves. The only clue we have is that one of Aerandil's guards mentioned that Aerandil is spending too much time with a whore at the Tall Mast Tavern. Valerius wants me to see if I can get any more information about Aerandil out of her. He showed me on my map that the tavern is located on the road to Morthal not far from Dragons Bridge."
By saying "I've never met a woman who doesn't like things made of gold" you can alternatively simply bribe her with 1,500 gold, which is quicker, if more expensive.
Whichever method is chosen to get the required information, Dianna tells you to go to the Winking Skeever in Solitude and speak to Maenen.
"I was able to find out that there may be an associate of Aerandil's staying at The Winking Skeever in Solitude. I must find him and see what more I can learn."
"Maenen reluctantly told me the slaves are shipped out of Skyrim from an old abandoned mine near an old shipwreck on the coast northwest of Solitude. He said a Bandit named Guunlaug heads up the operation. I should find this Bandit and get to the bottom of all of this."
There is a locked Chest by the Orphan's Tear and an unlocked one within the wreckage, underwater. After all the Bandits outside have been dealt with, enter the mine. There are five more Bandit Slavers and Guunlaug in here. In the first room there are an unnamed slave, Silena and Daening. Don't kill them. If you try and speak to them, they don't tell you anything.
Once all the Bandits and Guunlaug are killed, you need to free the slave prisoner who is locked in the slave pen. The door to the slave pen needs a key, the Slave Pen Key, which is on Guunlaug. Once the door is unlocked, the prisoner, Ingmarke, approaches you and speaks. He says that the slavers took him prisoner, along with his wife and son; Silena and Daening from the first chamber.
"I was ambushed by Aerandil and taken to his private ship. He told me he knew everything about what we have been doing. He also said that he was holding Marcus prisoner and that I must bring Valerius to the prison south of Helgen or that he would kill Marcus."
Falco says that he had no choice, as Aerandil has his sister and her children, and will kill them. Val replies that Falco is a fool, as his family are already dead or enslaved, and tells Korst to take Falco and lock him up.
You must now kill Aerandil and the other six Thalmor. You cannot cast any spells in the prison before this point, or even draw a weapon, so you may want to be in another room out of Aerandil's sight and let Val speak to him alone, so that you are able to prepare before Aerandil attacks you.
After you unlock the cage, Marcus speaks to you and then goes to check on Val. Marcus and Val have a conversation and some other Helgen troops arrive. After the conversation, Val dies (you cannot loot his body), a victim of the spell.
Marcus says that he and the others would like some time alone, and that there will be a service the next day for Val, but that they will not start the service without you.
"Valerius is dead. Marcus and the rest of the Keepers of Hattu will have a service for him tomorrow. I should meet them in Helgen in 24 hours."
After 24 hours, your log will update. During the waiting period, the Helgen Inn will be completely fixed.
Marcus is standing next to a pyre with Val's body on it in front of the Private Tower. Speak to Marcus, and then wait with the others. Marcus says some words and Cienna lights the pyre. This completes this quest, so now go and speak to Marcus to continue with A City on a Hill. A memorial will be erected where the pyre was.