First, you will need to become evil, which you can find in this guide:
Next, you need to listen to Hans' story, which is in this guide:
Here's a written walkthrough though.
1. As you finish the quest to becoming evil, and are still in the Arkos hideout, talk to a guy in a robe.
2. They will start a quest, asking you to kill Hans. Go to Darsov.
3. Enter Hans' house and listen to him. You will need to keep pressing "listen" for a long time until you can't anymore.