When you enter Markath for the first time, you’ll see a man killing a woman , then the guards come and take care of him. A man called Eltrys approaches you and "gives" you a letter asking you to meet him at the Shrine of Talos . This starts the Quest.
If you are quick, you can actually STOP the man from killing the woman (attacking him/interrupting him). This spares the woman’s life (her name is Margaret , she’s from Cyrodil) and she will just flat out give you a Silver Emerald Necklace once you talk to her.
Go to the Shrine of Talos, just like he asked you to do and speak to Eltrys . Ask him what he’s talking about and then it’s time to go find some answers (or evidence!). Leave the shrine and move to the Warrens. Once inside, speak to Garvey, who’s the first man you run into.
Ask him about Weylin to learn about his room. From here, either attempt to persuade, intimidate or bribe him to receive Weylin’s Room Key (alternately you could just PICK the door). Go to the last room on the right and enter Weylin’s room. Take the note from the chest and read it.
Cool! Time to find more evidence, then we look for Mr. N. Leave the Warrens and you’ll have to brawl Dryston. You find out about Nepos, Mr. N. Now go to the Silver-Blood Inn and speak to the wife of the owner. Ask about Margret and either persuade, intimidate or bribe her to get the key (They may just GIVE you the key as well, let me know what happened for YOU!).
Enter the room with the marker and check the End Table to find Margret’s Journal. Read it and now go to the Treasury House. Follow the marker and speak to Thonar. He will be very uncooperative until an attack occurs! Don’t just stand there, whip out your weapon and help! After the fight, speak to Thonar some more (who’s more chatty now) and then leave and head to Nepos’ house.
Speak to him and learn about his schemes. As you finish speaking to Nepos, he and the 2 other Forsworn will attack you. Kill them off ASAP. Be sure to loot them AND the house afterwards. Nepos himself has a lot of goodies and you can find an ILLUSION SKILLBOOK named "Mystery of Talara, Part 4" in one of the bedrooms.
Now leave and had back to the shrine to see Eltrys. As you arrive, some Markath Guards intimidate you. Agree to go with them to Cidhna Mines and this ends the Quest and starts automatically the next one.
Note: The next quest is " No one escapes Cidhna Mines ".