Two Sides of the Coin
This will start by you hearing a rumor about Jorundr taking Arnora Auria's money. Talk to Arnora with a disposition of 60+ and she will tell you that they used to be petty thieves until one big robbery, he was then caught and thrown into prison.
You will be then told to find out where the money is, no amount of talking will help so you have to be thrown into prison, steal something from her house to get caught, you may have to talk to Jorundr a few times, then he will tell you to kill Arnora and give him her amulet. Go to her, you can either kill her (it will count as murder and you will get in the Dark Brotherhood), take her key and get the real amulet from the chest or you can let her live and she will give you the key to the chest. Get the amulet and give it to him, e will tell you to get the treasure either way, if you saved Arnora, you will find someone called Tyrellius, he says he killed Arnora and will get the treasure, kill him, then get the treasure, there should be some jewels an 2 skill books there.