After completing a number of jobs in Windhelm (5 or so, I think…), Delvin will have this "Special Job" for you. A wealthy merchant from Windhelm named Torsten Cruel-Sea has requests our assistance. Go see him and he’ll explain that his daughter Fjotli was slain and robbed, and that after quite some time he found out it was a Thieves Guild from Summerset Isle called "The Summerset Shadows". It seems that they are trying to enroach upon our turf! We can’t have that!
Our next objective will be to "Speak to Niranye". Niranye is one of the stall vendors inside of the city, so go find her and speak to her. Ask her about Fjotli and then tell her you know she was involved. After that, you can try your hand at an INTIMIDATE option or a PERSUADE option. Once you pass one of those Niranye will spill the truth: she is a FENCE that has been coerced into working with the Summerset group under threat of death. She will divulge where the leader, Linwe, is hiding: Uttering Hills Cave.
Do NOT use the response "I’ve had enough of this" as it will cause Niranye to attack you! We can use her later, we don’t need her dead!
If by chance you can’t pass EITHER the INTIMIDATE or PERSUADE options, you can get through this another way. Follow the box if you want to find out how! Just an FYI, it does require you to be able to pick a MASTER lock!
So you can’t use Persuade or Intimidate. Damn. Don’t fret too much, and excuse yourself from the conversation (the bottom option: "My Mistake"). You’ll be given a new objective to "Discover Leverage to sway Niranye. To do this we need to break into her house. Note that you can pickpocket her key off of her as well as a "Darkwater Pit" key. Do so if you don’t feel like lockpicking all that much.
Niranye’s house is the first house on the right as you enter Windhelm and take an immediate right. Go break into it and you’ll find… nothing? However, there is a HIDDEN PANEL on one of the walls in the dining room, so find it and open it. Down the stairs is the door to the basement, which is a MASTER lock. I hope you’re good at lockpicking!
Once you’re in the basement you’ll find Niranye’s safe against the far wall. The Darkwater Pit key can open the safe, by the way, so either use it or pick the lock (an Expert lock for me). You’ll now have two letters from Linwe to Niranye. Go show her these and she’ll reveal the hideout just as if you passed the Intimidate or Persuade tests…
Now that we know where to go, you can look at your map and see that the Uttering Hills Cave is just southwest of Windhelm. Make your way there and get ready to bring justice to this Thieves Guild. You’ll of course be attacked on sight, so its only right to defend yourself. And by defend yourself I mean kill every last person you come across. There are two guards outside of the cave so kill them and enter.
Head inwards until you see an opening with a pine growing WAY above you. Just beautiful! Now brutally slay the guards to your left and right. Take either path downwards to a camp site and kill two more guards there. Open the wooden door and continue on. Head down the steps and you’ll see a guard up ahead. There are actually several guards in this area (about 4) as well as Linwe himself who is MUCH tougher than any of these "Summerset Shadows". Take up a good defensive position (like on the stairs) and kill them all. Now feel free to loot the place. Linwe is the prize of course, as he has the locket we need as well as a set of thieves armor that is enchanted. There’s also a chest in one of the cubbys by the alchemy lab.
Head further in to see their jail and banner. Once you get near the banner you will get an optional objective to destroy it, which you can easily do by putting it to the flame. To the right is a bedroom with a chest and a ONE HANDED SKILLBOOK ("Mace Etiquette").
Once you’re done looting the place, head back out to the world map and go find Torsten. He’ll be thankful and will promise to help out the Thieves Guild in Windhelm. He’ll also give you an Major Ring of Archery as thanks. Head back to Delvin and report in. Congratulations! Now go do more Thieves Guild missions!