Dragon Age 2 - Alone is a companion quest for Fenris in Act 3, a continuation of the storyline for Fenris. For this walkthrough, players will encounter Danarius, Fenris' former master and owner, and have to decide to either hand Fenris over to him, or refuse and fight Danarius.

1. To receive the quest, speak with Fenris in his mansion in Act 3. You will most likely have to have already finished the previous companion quests for Fenris to be eligible for this one.
2. Accept the quest, add Fenris to your party, and go to the Hanged Man pub at Day.
3. Here, the player will be surprised by the appearance of Danarius, Fenris' owner and "master" (Fenris was his slave before escaping and joining your group). 
4. You will have 2 choices here; to hand Fenris over to Danarius, or to refuse and face Danarius in combat.
5. If you choose the refuse option, you will face 3 waves of enemies, followed by Danarius himself.
6. The first wave is quite easy. Just kill the slavers.
7. Kill the Rage Demon for the second wave.
8. Kill the undead for the third wave, they are quite weak.
9. For the Danarius fight, simply put everyone on Danarius and bring him down. He may spawn some undead, but they are very weak and can be ignored. Use interrupt abilities to stop Danarius from casting any spells.
10. After the fight, you can decide to let Fenris kill his sister, or to convince him to let her go.